The Magazine of the Arnold Arboretum
VOLUME 71 • NUMBER 1 • 2013
Amoldia (ISSN 0004-2633; USPS 866-100)
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Nancy Rose, Editor
Andy Winther, Designer
Editorial Committee
Phyllis Andersen
Peter Del Tredici
Michael S. Dosmann
William (Ned) Friedman
Kanchi N. Gandhi
Copyright © 2013. The President and
Fellows of Harvard College
Tl-e ARNOLD
ARBORETUM
of HARVARD UNIVERSITY
CONTENTS
2 Mutants in our Midst
William E. Friedman
15 Rediscovering Rhododendron Dell, Part 2
Kyle Port
26 The World of Mosses
Stephanie Stuber
36 Chamaecyparis obtusa 'Chabo-hiba'
877-37: A Venerable Survivor
Peter Del Tredici
Front cover: Mountain laurel {Kalmia latifolia] nor-
mally bears cup-shaped flowers like these, but Arnold
Arboretum Director William (Ned) Friedman writes
about a fascinating mutant form at the Arboretum
(starting on page two). Photo by Nancy Rose.
Inside front cover: The common name for Polytrichum
commune is haircap moss, which refers to the abun-
dant hairs on the calyptra of its showy sporophytes.
Photo by Stephanie Stuber.
Inside back cover: Part of the Larz Anderson Bonsai
Collection, Chamaecyparis obtusa 'Chabo-hiba' acces-
sion 877-37 arrived in the United States from Japan 100
years ago. Photo by Dave Henderson.
Back cover: Expanding flower buds form a striking
pattern on Rhododendron 'Cynthia' accession 813-72-B.
Photo by Kyle Port.
f AUG 2 8 2013 J
Mutants in our Midst
William E. Friedman
What is horticulture? At its core, it is
a human celebration, whether con-
scious or unconscious, of the very fact
of evolution. It is thousands of years of detect-
ing and rejoicing in the rare: the selection of the
novel form that somehow pleases the human
aesthetic or serves to feed the world. Although
often overlooked, many of the wonderful horti-
cultural varieties that grow in botanical gardens
(as well as in backyard gardens) are premier
examples of the amazing and ongoing process
of evolution: random mutations that lead, on
the rarest of occasions, to novel and desirable
biological characteristics — as opposed to novel
and neutral or undesirable characteristics.
Charles Darwin was an avid consumer of hor-
ticultural literature and information, and was a
frequent correspondent with the most eminent
horticulturists of the nineteenth century. Over
the course of his life, he wrote 55 notes and arti-
cles in the Gardeners’ Chronicle and Agricul-
tural Gazette, one of the most widely circulated
horticultural periodicals of his time. He cov-
ered everything from how pea and bean flowers
are pollinated (Darwin 1857, 1858, 1866) to the
origin of variant forms of roses in cultivation
(Darwin 1868). He wrote of his observations
of and interest in the origin of double-flowered
forms (Darwin 1843) and variegated leaves (Dar-
win 1844). No horticultural phenomenon was
beyond his interest. Indeed, Darwin looked to
the world of horticulture and plant domestica-
tion in order to gain critical insights into the
generation of variation and the process of natu-
ral selection that underlie evolutionary change.
In essence, Darwin was intensely interested in
mutants in our midst.
EVOLUTION AT THE ARBORETUM
The Arnold Arboretum of Harvard University
hosts a remarkable collection of more than
15,000 accessioned woody temperate plants
distributed in over 2,000 different species. This
Charles Darwin wrote about many horticultural topics
including variegated pelargoniums, which were very
popular in the Victorian era. 'Mrs. Pollack', seen here,
was introduced in 1858.
"Florists have attended in some instances
to the leaves of their plant, and have thus
produced the most elegant and symmetrical
patterns of white, red, and green, which, as in
the case of the pelargonium, are sometimes
strictly inherited."
— Charles Darwin, The Variation of Animals
and Plants Under Domestication, 1868
living collection contains wild-collected trees,
shrubs, and vines, as well as a spectacular set of
horticultural varieties whose very presence is
the result of human discovery and propagation
of desirable variants. Many of these horticul-
tural varieties are the result of the never-ending
process of spontaneous mutations that occur
in all organisms and serve to create novel
GEOFF BRYANT
Variety, Form, or Cultivar?
HOW TO NAME a variant plant is the topic of some taxonomic debate and often results in multiple
versions of the plant's name. As taxonomic understanding and interpretation changes through the
years it often results in changed nomenclature, reflected in the International Code of Nomenclature
and the International Code of Nomenclature for Cultivated Plants. A quick reference search finds the
white-flowered redbud mentioned in this article listed as Cercis canadensis var. alba, Cercis canaden-
sis f.[forma] alba, or Cercis canadensis 'Alba'(a cultivar name). The same range of synonyms are found
for the mutant Kalmia latifolia (var. polypetala, f. polypetala, or 'Polypetala') featured later in the
article. To add to the confusion, in common usage the words "variety" and "form" are often broadly
applied ("I like pink varieties of roses") or used when referring to a cultivar. For this article, I have
used the scientific names as they appear in the Arboretum's collections database.
Eastern redbud [Cercis canadensis) blooms throughout its canopy, producing a spectacular spring display.
traits — the very stuff of evolution. These vari-
ant plants, referred to as "sports," arise in a sin-
gle generation and have undergone a dramatic
change in phenotype (the biological properties
of the organism) from the parent plant and spe-
cies. Typically, sports are discovered as a single
branching system on a tree or shrub that dif-
fers significantly in its morphology, coloration,
or other biological properties from the rest of
the parent plant. The source of the biological
novelty is random mutation, and subsequent
vegetative propagation (e.g., grafting, rooting of
cuttings, tissue culture) allows the new form to
be cloned for further dissemination.
Since arriving at the Arnold Arboretum in
January 2011, I have fallen in love with these
wonderful horticultural results of random
genetic mutations and the creation of novelty
PAUL W, MEYER, MORRIS ARBORETUM
4 Ainoldia71/l • August 2013
in plants. And in turn, I have come to see the
Arboretum (and all botanical gardens) as among
the best places to actually observe evolution,
and importantly, how evolution works. A walk
in any woodland would indeed expose the ram-
bler to mutant forms of plants, but most of
these would be so subtle as to evade the senses
of all but the most acute observer. On the other
hand, a walk through the Arboretum essentially
concentrates the opportunity to witness the
results of evolution — many of our horticul-
tural gems are representatives of the even rarer
forms of mutations that are dramatic and easily
observable. In this article, I will examine two
cases of mutants in our midst at the Arboretum.
Each is the result of what is likely to be a single
genetic mutation that caused a major change in
the color or morphology of the plant that bears
the aberrant copy of the gene.
THE REDBUD AND THE ORIGIN OF
NOVEL FLOWER COLOR
"A long list could easily be given of "sporting
plants;" by this term gardeners mean a single
bud or offset, which suddenly assumes a new
and sometimes very different character from
that of the rest of the plant. Such buds can
be propagated by grafting, Ac., and sometimes
by seed. These "sports" are extremely rare
under nature..."
Charles Darwin, On the Origin of Species,
1859
"Many cases have been recorded of a whole
plant, or single branch, or hud, suddenly pro-
ducing flowers different from the proper type
in colour, form, size, doubleness, or other char-
acter. Half the flower, or a smaller segment,
sometimes changes colour."
Charles Darwin, The Variation of Animals
and Plants under Domestication, 1868
The eastern redbud, Cercis canadensis (pea
family, Fabaceae), is a widely distributed small
tree species native to the eastern and midwest-
ern United States from Connecticut south to
Florida and over to Oklahoma and parts of
Texas. Every spring, it can be counted on for
its clusters of pink and magenta flowers that
appear throughout the leafless canopy just prior
to the production of new leafy shoots. The
Arnold Arboretum has more than twenty acces-
sioned specimens of Cercis canadensis. One of
these trees (accession 10-68-B), however, has
had something remarkable
occur — it has undergone a
spontaneous (and random)
mutation that changes
the color of the flowers
from the normal ("wild-
type") pink and magenta
to mostly white.
For several decades after
its establishment in the
Arboretum collections,
this specimen produced
the characteristic clusters
of pink and magenta flow-
ers on all of its two-year
and older woody branches.
Fiowever, beginning about
ten years ago (see below
for details on how this was
determined), one of the
branches on this tree began
to produce flowers that are
About a decade ago, a mutation that eliminated most of the synthesis of red pigmenta-
tion in flowers occurred on a branch of an Arboretum redbud (Cercis canadensis, acces-
sion 10-68-B ), producing pink-tinged white flowers on that branch.
WILLIAM E. FRIEDMAN
Mutants in our Midst 5
This cluster of flowers shows both the normal (pink and
magenta) and the mutant (whitish) forms found on the Arbore-
tum’s mutant redbud.
mostly, but not entirely, white. It was not, how-
ever, until the spring of 2009 that these aberrant
flowers were first noticed by Arboretum staff.
The flowers are beautiful, and novel and rare
in a way that every lover of new horticultural
forms can appreciate. Now, every year, this red-
bud continues to produce the typical pink and
magenta flowers on most of its shoot systems,
with whitish flowers on a single lateral set of
branches that bear the mutant gene that results
in altered flower color.
Interestingly, this is by no means the first
horticultural variant of the eastern redbud to
sport white flowers. A widely grown one, Cer-
cis canadensis 'Alba' (often referred to as C.
canadensis f. alba from its earlier botanical
description) can be found in gardens through-
out the United States. It has pure white flowers,
with no trace of red pigmentation. Although it
has not been scientifically studied, it is very
likely that the mutation that created 'Alba'
was one that "broke" or entirely suppressed
the expression of the biochemical pathway to
produce red pigmentation in these plants. Even
young leaves, which typically have a purplish
(Top to bottom) normal redbud flower with full red pigmenta-
tion; one of the mutant flowers, with pink splotches on the
petals and a lighter pink calyx showing that some red pigmen-
tation is still expressed; and a flower of 'Alba', with distinctly
green sepals and white petals lacking any red pigmentation.
WILLIAM E. FRIEDMAN
WILLIAM E. FRIEDMAN
6 Arnoldia 71/1 • August 2013
or reddish hue in normal eastern redbuds, are
green in 'Alba', suggesting that red pigmen-
tation from anthocyanins is lacking from
these plants. Another white-flowered cul-
tivar of eastern redbud, 'Royal White', also
lacks red pigmentation in its flowers and
young emerging leaves.
Both 'Alba' and 'Royal White' arose on sepa-
rate occasions when a parent plant underwent
a spontaneous mutation that disabled the bio-
chemical pathway that produces the red pig-
ment anthocyanin. 'Alba' originated in the
nursery of John Teas and Son in Carthage,
Missouri, around the turn of the last century
(Rehder 1907; Anonymous 1922). Both the
Arnold Arboretum and the Missouri Botanical
Garden acquired this cultivar in 1903. Sadly,
the Arboretum's specimen perished in 1930,
perhaps a reflection of the greater sensitivity
to cold of this cultivar. 'Royal White' was dis-
covered as a seedling in Bluffs, Illinois, in the
1940s. For each of these white-flowered redbud
variants, it might well have been the case that
had no one observed the mutant form, natural
selection would have culled this variant from
the gene pool as a consequence of its being less
fit than its red-pigmented cousins. Flower color
is an important biological attribute and in the
case of redbuds in a state of nature, almost cer-
tainly affects rates of insect
pollination. A variant lacking
the standard red pigmentation
might still be visited by bees
and other insects, but per-
haps at lower rates. In addi-
tion, anthocyanins may also
serve as photoprotectants for
plants. Young leaves, while
expanding to mature size, can
be very sensitive to high light
levels, and red pigmentation
can serve an important role
in helping these tender leaves
to avoid being sunburned and
permanently damaged (Close
and Beadle 2003).
In the case of the remark-
able eastern redbud with the
whitish flowers at the Arbo-
retum, the genetic mutation
has caused these flowers to lose most, but not
all, of their red pigmentation. A careful exami-
nation of the mutant flowers shows that there
is still red pigmentation present, although in
significantly lesser amounts. The calyx (the col-
lective term for the sepals of a flower) is pink
with streaks of green. This is similar to the
calyx of the normal flowers, except that in a
normal flower (found on the rest of the tree),
the calyx appears to contain more anthocyanins
that render it more deeply pigmented.
The petals of the mutant redbud flowers also
show something rather interesting. At first
glance the flowers appear white, but a closer
look under the microscope demonstrates that
there are often small patches of pink pigmen-
tation on the petals. The banner petal (upper
center petal) often displays relatively strong
expression of magenta in radiating streaks
that lie between the veins of this specialized
petal. Interestingly, returning to examine the
normal flowers reveals that the banner petal,
while clearly pink, also has more intense
zones of deep magenta that radiate out and lie
between the veins. This is true on the tree's
non-mutant flowers, as well as on flowers of
other standard redbuds (Robertson 1976). A
pattern of red streaking is characteristic of what
are commonly called nectar guides, displays
Mutants in our Midst 7
of pigmentation that help insect pollinators
orient properly as they approach the flower dur-
ing pollination. Nectar guides are much the
same as the lighting on an airport runway, help-
ing the airplane pilot to properly approach the
landing strip.
Finally, in the mutant redbud flowers the
female reproductive parts, particularly the style
and stigma, differ in pigmentation from the
wild type. In normal redbud flowers, the style
displays a reddish color, as a consequence of
the expression of the biochemical pathways to
create anthocyanins. Under the microscope, it
becomes evident that the mutant flowers have
styles that lack any obvious red pigmentation.
What does all of this mean? It suggests
that unlike 'Alba' and 'Royal White', which
appear to have entirely lost the ability to cre-
ate anthocyanins (at least in the flowers and
young leaves), the Arboretum variant has a
mutation that alters where the anthocyanins
are produced. In other words, it still makes red
pigmentation, but the cellular machinery that
might otherwise produce this pigmentation
throughout the petals and the style is no longer
turned on in these places.
How do we know when and where this
remarkable single mutation occurred in the
Arboretum redbud variant? The answer lies in
a basic knowledge of how plants grow and a
specific knowledge of an unusual pattern of
flowering that can be found in redbud trees. At
the tip of every branch of every tree, there is a
small group of cells that remains perpetually
embryonic and undifferentiated. These cells
form the apical meristem, and are similar to
stem cells in humans. Every year this small
population of cells divides, and in dividing cre-
ates the new tissues that will differentiate into
stems and leaves. If a mutation occurs in one
of the cells of the apical meristem, this muta-
tion may come to populate some or all of the
cells, and hence the differentiated stem, leaf,
and flower cells that are descended from this
mutant apical meristem.
In the Arboretum's mutant redbud, the muta-
tion that reduced the production of anthocya-
nins in the flowers of this tree can be found on
a set of branches that are all descended from an
original mutant meristem of the growing tip of
a single shoot. The ability to determine when
this mutation occurred in a shoot apical meri-
stem can be deduced because of a specific and
somewhat unusual characteristic of all redbud
trees. Redbuds exhibit a phenomenon known as
cauliflory (Owens et al. 1995). Translated liter-
ally, cauliflory means flowering on stems. How-
ever, in botanical usage, cauliflory refers to the
production of flowers on older woody stems.
A careful examination of redbud trees reveals
Z
Q
This banner petal of a mutant flower clearly shows magenta lines that act as nectar guides for insects (a close-up of
the nectar guides under the compound microscope is seen at right).
8 Arnoldia71/l » August 2013
Redbud's trait of cauliflory (production of flowers
on older stems) helped with determining when the
mutation that eliminated most of the synthesis of red
pigmentation in flowers occurred in this tree.
clusters of flowers that can be found along all
of the branching systems (except for the cur-
rent year's new shoots) and even the trunk of
the tree. It is the phenomenon of cauliflory
that makes redbuds so spectacular when they
flower. Rather than having flowers restricted
to the newest growth of the plant, flowering
in redbuds is spread throughout the entire leaf-
less canopy.
In the photo above, you can see two clusters of
flowers on an old branch of our mutant redbud
tree. One of the clusters of flowers is wild type,
with a magenta calyx and typical pink petals.
Just inches away, another cluster of flowers can
be seen with a lighter pink calyx and petals that
are almost exclusively white. This tells us that
the population of cells making new magenta
and pink flowers each year are different from
the nearby population of cells making largely
white flowers. Years ago, when the shoot apical
meristem was growing at this point, the muta-
tion that reduced production of anthocyanins
in flowers occurred. From that point forward,
all of the cells of the subsequent shoots con-
tained the mutation creating the whitish flow-
ers. Because of cauliflory, the tree continues to
produce flowers on parts of the shoot system
that in other kinds of plants would no longer
produce flowers. And this allows us to infer that
about ten years ago, a mutation occurred in the
cells of the growing tip of the shoot when it was
located between the typical cluster of magenta
and pink flowers and the more distal cluster of
mutant white flowers.
THE MOUNTAIN LAUREL AND THE
ORIGIN OF NOVEL FLOWER FORM
"We have before us a novel and specially inter-
esting monstrosity which is described by these
terms. It was discovered by Miss Bryant, at
South Deerfield in this state [Massachusetts],
and we are indebted to her, through a common
friend, for the specimens before us. Among the
shrubs of Kalmia latifolia which abound in a
swamp belonging to Col. Bryant, a few have been
noticed as producing, year after year, blossoms
in singular contrast to the ordinary ones of this
most ornamental shrub, and which, indeed, are
more curious than beautiful. The corolla, instead
of the saucer-shaped and barely 5-lobed cup, is
divided completely into five narrowly linear
or even thread-shaped petals. These are flat at
the base, and scarcely if at all broader than the
lobes of the calyx with which they alternate,
but above by the revolution of the margins they
become almost thread-shaped, and so resemble
filaments. This resemblance to stamens goes
further; for most of them are actually tipped
with an imperfect anther; that is, the corolla
is separated into its five component petals, and
these transformed into stamens."
Asa Gray, 1870
Kalmia latifolia, mountain laurel, is a member
of the heath family (Ericaceae) and close kin
to rhododendrons and azaleas. It is a beauti-
ful evergreen shrub whose natural distribution
extends from the panhandle of Florida north to
Maine and southern Ontario. In spring, moun-
tain laurels produce an abundance of flowers
in terminal panicles. In the wild, flowers of
Kalmia latifolia are white to pink, with showy
cup-shaped corollas. Hundreds of cultivars have
been selected; these variants have flowers rang-
ing from white to deep red, many with banded
or speckled patterns. But, the "monstrosity"
described above (initially as Kalmia latifolia var.
monstwsa, later as K. latifolia f. polypetala, and
now generally referred to as the cultivar Toly-
petala') is not a color mutant. Rather, it is a vari-
ant with an altered morphology of the petals.
Instead of forming a sympetalous (fused sets of
petals) corolla, 'Polypetala' has narrow, unfused
individual petals. This is the form of mountain
laurel first described by Harvard Professor of
Botany Asa Gray in 1870, as a consequence of
the keen collecting eye of one Miss Mary Bryant
of South Deerfield, Massachusetts.
It did not take long before specimens of this
unusual morphological mutant came to Har-
vard University. A specimen of Kalmia latifo-
In this inflorescence of Kalmia latifolia 'Polypetala'
many of the flowers have yet to open. The dark red
coloration at the tips of the filiform petals is associated
with the unusual production of pollen-producing anthers
on these mutant petals. Also note the reflexed normal
stamens jutting out between the petals.
Inflorescences of Kalmia latifolia 'Polypetala' create a markedly altered and attractive appearance when the plant is
in flower (the plant seen here is the original 1885 accession from South Deerfield, Massachusetts). Flowers of a normal
("wild-type") K. latifolia are seen at far left in the photo.
10 AinoldiaJl/l » August 2013
Rudolph Blaschka made drawings for glass models from,
several plants at the Arnold Arboretum, including Kalmia
latifolia 'Polypetala' (labeled as var. Monstrositat on the draw-
ing at right). The exquisite glass models of the normal (top) and
mutant (bottom) forms of mountain laurel can be seen at the
Harvard Museum of Natural History.
"V/ fv>t v:
I
DRAWINGS: COLLECTION OF THE RAKOW RESEARCH LIBRARY, THE CORNING MUSEUM OF GLASS
Mutants in our Midst 1 1
lia Tolypetala' from the Harvard University
Herbaria notes that it was collected in the
Botanic Garden at Harvard (in Cambridge) in
1884. Another 1891 herbarium sheet in the Har-
vard University Herbaria comes from a grafted
specimen that was introduced into the Arnold
Arboretum in 1885 (accession. 2458). Finally,
and quite wonderfully, one of the extraordinary
models in Harvard's famed glass flowers (for-
mally, the Ware Collection of Glass Models of
Plants) was based on observations and collec-
tions of the Arboretum specimen of Kalmia
latifolia Tolypetala'. In the summer of 1895,
Rudolph Blaschka — of the father (Leopold) and
son (Rudolph) team that created the glass flow-
ers— came to the Arboretum to sketch and
observe this mutant pioneer. The glass model
of Kalmia latifolia Tolypetala' (one of over
800 models created by the Blaschkas between
1886 and 1936) can be viewed at the Harvard
Museum of Natural History. And, after all of
these years, six of the seven original living
plants from the 1885 accession (2458-A, B, C,
E, F, G) still survive and thrive on the grounds
of the Arboretum.
In 1907, another cluster of mountain laurels
with unfused petals was found along roadsides
in Leverett, Massachusetts, near Mount Toby
(Stone 1909). The mutant petals of these plants
were reported not to produce anthers at their
termini, as is the case with the 'Polypetala' dis-
covered by Miss Bryant and first described by
Asa Gray. Arboretum botanist Alfred Rehder
suggested that this discovery was evidence of
the independent origins of these petal mutants
in different naturally occurring populations
(Rehder 1910). However, it is possible that this
description was in error. In the University of
Massachusetts Herbarium, there are six speci-
mens of the Tolypetala' form of mountain lau-
rel (in flower) that were collected between 1910
and 1932 on Mount Toby, and all of them show
anthers at the tips of the mutant petals. Perhaps
these oddly placed anthers were not initially
observed in the report from 1909. Nevertheless,
it is worth noting that Tolypetala'-like forms of
Kalmia latifolia have also been found growing
in the wild in North Carolina (Ebinger 1997)
and elsewhere. These variants appear to be fun-
damentally different from those of the South
Deerfield and Mount Toby populations, as they
are reported to lack anthers on the tips of the
unfused (apopetalous) petals. Clearly there are
at least two different and independently formed
(evolved) variants with the unifying feature of
forming unfused petals — not unlike the multiple
evolutionary origins of white-flowered redbuds.
Asa Gray's description of the Tolypetala'
type of Kalmia refers to the notion that the pet-
als have been "transformed into stamens." In
evolutionary terms, this is a statement worth
examining. Close observation with a hand lens
(or under the microscope) of the "petals" of the
South Deerfield plant reveals that each one bears
a pair of pollen-producing structures at its distal-
most end (collectively, an anther). As might be
expected, pollen can be found within and then
dispersed from these anomalous anthers. Nor-
mally, the stamens of Kalmia latifolia comprise
a long filament terminated by a reddish anther
that produces pollen. A defining characteristic
of the floral biology of Kalmia species is that the
ten stamens insert themselves into ten pouches
in the petals of the cup-like corolla, creating a
mechanical tension. Visitation by an insect pol-
linator trips the catapult and the anther flings
pollen with enough force to throw it three to
six inches away from the flower, but usually
directly onto the body of the pollinator, where
it will be transported to the next flower to effect
pollination (Ebinger 1997).
In the Tolypetala' Kalmia from South Deer-
field, the "petals" still produce a pouch about
midway along the length of the organ. However,
the disruption to the normal morphology of
these flowers precludes the proper insertion
of the ten normal stamens into these pouches.
Thus, as the flower expands towards anthesis
(the opening of the flower), the ten normal
stamens proceed through their typical pattern
of physical reflexing, but never find the petal-
borne pouches. The "petals" also bear much
of the typical pinkish-red markings that create
some of the brilliant spots or circumiferential
bands on the corolla of normal flowers. As such,
the South Deerfield Tolypetala' "petals" may
best be thought of as chimeric organs — part
petal and part stamen — while some of the other
Tolypetala'-like variants that lack anthers on
their unfused petals may best be viewed as
12 Ainoldia71/l • August 2013
mutations that have only changed the form of
the petals from hroad and fused to more narro'w
and unfused.
Interestingly, over the course of the last thirty-
five years, molecular biologists have uncovered
some of the basic genetic controls that deter-
mine whether a floral organ will differentiate
into a sepal, petal, stamen, or carpel (the female
seed producing organ). The scientific literature
is filled with instances where geneticists have
created mutant forms of flowers in which pet-
als have been replaced with stamens, or sta-
mens have been transformed into carpels (Coen
and Meyerowitz 1991; Mathews and Kramer
2010). Along the way, floral mutants have also
been created in the laboratory with chimeric
or hybrid structures that blend petals with sta-
mens, as appears to be the case in the South
Deerfield 'Polypetala'. The floral mutants that
scientists have created in the laboratory are a
wonderful echo of the myriad naturally occur-
ring mutations in nature that have produced
many of our beloved horticultural variants.
As with the case of the Arboretum's mutant
redbud, it is possible that a mutation in a
"normal" mountain laurel growing in South
Deerfield, Massachusetts occurred in a shoot
apical meristem that then produced a branching
system bearing the mutant gene. From there,
seeds produced by the mutant branching sys-
tem might have yielded descendants with the
novel form of corolla. Alternatively, a muta-
tion could have occurred either in the gamete
lineage or young embryo of a mountain laurel
plant, as appears to have been the case with the
'Royal White' cultivar of redbud trees, where
the aberrant type arose as a seedling. In this
case, a new variant plant would have appeared
in a single generation with flowers that all bore
the linear, unfused petals.
If this seems unlikely, it is worth noting
that Queen Victoria, who was a carrier for the
genetic mutation that confers hemophilia (a
carrier does not have hemophilia, but can trans-
mit the disease to her descendants), appears
to have acquired a mutant copy of this gene
either as a gamete or as a zygote (assuming she
was not the illegitimate daughter of a hemo-
philiac biological father) or to have undergone
a mutation in her own cells that produced eggs
(Potts and Potts 1995). We know this because
A bee with heavily laden pollen baskets on its hind legs visits
flowers of a Kahnia latifolia with the normal cup-shaped, fused-
petal corolla. Note the ten pollen-producing anthers held in
pockets on the corolla; physical contact (typically by a pollina-
tor) unsprings the anthers, which catapult a shower of pollen.
A 'Polypetala' petal (top) shows a stripe of pink pigmentation that
correlates with the inner pink ring seen in normal flowers.
The red patch at the right (distal) end is where the "misplaced"
pollen-producing anthers form. A normal pollen-producing sta-
men from the mutant flower is seen below the petal.
In normal Kahnia latifolia flowers the ten stamens reflex back-
wards and insert into the ten pockets in the cup-shaped corolla,
but in 'Polypetala', seen here, they are unable to find their
normal spot and reflex backwards between the separate petals.
Note the deep red anthers at petal tips.
PHOTOS BY WILLIAM E. FRIEDMAN
Mutants in oui Midst 13
family history and modern genetics make clear
that the gene for hemophilia did not exist in
her family prior to her conception. Mutations
happen in gametes (or gamete-producing cell
lineages); and zygotes and the organisms that
develop from the act of fertilization will exhibit
the consequences of the new mutation. Recent
sequencing of whole genomes of human fami-
lies indicates that each of us carries roughly 75
new simple genetic mutations ("single nucleo-
tide variants" in the parlance of geneticists) that
neither of our parents was born with (Campbell
et al. 2012; Kong et al. 2012).
Whether the mutation that created a new
chimeric corolla form in the South Deerfield
Kalmia latifolia took place in the immediate
decades before Miss Bryant found the mon-
strous plants, we will never knov/. It could be
that this mutation was present in this local
population of mountain laurels for hundreds if
not thousands of years, unseen by human eyes.
And for all we know, this mutation might ulti-
mately mark the beginning of a new species of
Kalmia over the course of time. In either case,
it took a wandering (and observant) natural-
ist to discover this product of the evolutionary
process, this biological gem, and bring it to the
attention of a professional botanist. One can
only imagine the delight of Miss Bryant upon
finding this unique type of mountain laurel!
CLOSING THOUGHTS ON BOTANICAL
GARDENS AS SHOWPLACES OF
EVOLUTION
And so we come back to the concept of botani-
cal gardens and horticultural variants as exem-
plars par excellence of the process of evolution.
In populations of redbuds around the world,
mutations are constantly occurring. The same
is true for mountain laurels (and humans).
These mutations might create selectively
favored traits such as resistance to drought, or
tolerance to cold, neither of which can be seen
by the human eye. Most of the -genetic muta-
tions in redbuds and mountain laurels (indeed,
all organisms) will probably have little if any
effect on the fitness of the plant. Some will be
deleterious, and these genes will ultimately be
purged from the population. In evolutionary
terms, it is always easier to "break" something
than to create a novelty that improves fitness.
Botanical gardens are filled with examples of
spontaneous mutations, many of which evolved
and were discovered in our own lifetimes.
These are the very same kinds of mutations
that occur constantly in nature and have served
as the raw materials that gave rise to humans,
oak trees, and plasmodial slime molds — all
descended and transformed over the course of
billions of years from a single-celled common
ancestor of all of life on Earth. The raw ingre-
dients of evolution writ large are all around
us. And if we look carefully, we can observe
the process of evolution by simply walking
through a botanical garden, or one's own back-
yard. Mutant forms of redbud and mountain
laurel, as well as myriad other "sports," are an
important reminder that we live in a beautiful
and profoundly evolutionary world.
References
Anonymous. 1922. White red-bud. Missouri Botanical
Garden Bulletin 10(6); 110.
Campbell, C.D. et al. 2012. Estimating the human
mutation rate using autozygosity in a founder
population. Nature Genetics 44: 1277-1281.
Close, D. C. and C. L. Beadle. 2003. The ecophysiology
of foliar anthocyanin. The Botanical Review
69; 149-161.
Coen, E. S. and E. M. Meyerowitz. 1991. The war of the
whorls: genetic interactions controlling flower
development. Nature 353: 31-37.
Darwin, C. R. 1843. Double flowers-their origin.
Gardeners’ Chronicle and Agricultural Gazette
36: 628.
Darwin, C. R. 1844. Variegated leaves. Gardeners'
Chronicle and Agricultural Gazette 37: 621.
Darwin, C. R. 1857. Bees and the fertilisation of kidney
beans. Gardeners’ Chronicle and Agricultural
Gazette 43: 725.
Darwin, C. R. 1858. On the agency of bees in the
fertilisation of papilionaceous flowers, and
on the crossing of kidney beans. Gardeners’
Chronicle and Agricultural Gazette 46: 828-
829.
Darwin, C. R. 1866. Cross-fertilising papilionaceous
flowers. Gardeners' Chronicle and Agricultural
Gazette 32: 756
Darwin, C. R. 1868. The Variation of Animals and Plants
Under Domestication. John Murray: London.
Ebinger, J. E. 1997. Chapter 2: Laurels in the Wild, pp.
29-51. In; Kalmia: Mountain Laurel and
Related Species. R. A. Jaynes (author). Timber
Press: Portland, Oregon.
POSTSCRIPT: One question that lingered after all of the
historical research on Kalmia latifolia 'Polypetala' was
whether any of the mutant plants (or their descendants)
that were originally found on Colonel Bryant's property
were still in existence. A map of the South Deerfield,
Massachusetts, area from 1871 showed exactly where
this property was located. Fortunately, this map could
be cross-correlated with modern maps to show where
Miss Bryant collected the mutant plants.
On June 22, 2013, I drove to South Deerfield to hunt
the wild mutant Kalmia. The old home that once
belonged to Colonel Bryant still stands and is well cared
for. Regrettably, the land around the original six acres
has not had a kind interaction with humans. The bar-
ren area on the other side of the brook was home to a
pickle factory for many years. The town also installed
a major sewer line that is buried alongside the brook.
While I found lots of poison ivy and a modest amount of
undergrowth beneath some maples and hemlocks, there
were no Kalmia plants, mutant or otherwise, to be seen.
After my visit to South Deerfield, I drove around the
base of Mount Toby. There, I spotted several spectacu-
lar populations of mountain laurel in full bloom. My
ramble in the woods did not turn up any mutant flow-
ers. Next year, with a bit of time and coordination with
the University of Massachusetts Herbarium, we will
try to explore the Mount Toby area and search more
thoroughly for the 'Polypetala' form of Kalmia latifolia.
The loss of the mountain laurel population from
which Miss Bryant collected the 'Polypetala' mutant is
a stark reminder of the incredible importance of botanical gardens as refugia for rare and endangered
plants, whether entire species, threatened local populations, or unusual mutant forms. It is a very
fortunate thing that Miss Bryant's monstrosity was propagated and cared for at the Arnold Arbore-
tum. Otherwise, it might well have disappeared from the face of the earth without a second thought.
This section from an 1871 map of South Deerfield,
Massachusetts, shows Colonel Bryant's property,
where the mutant mountain laurel was discovered,
near the center.
Kong et al. 2012. Rate of de novo mutations and the
importance of father's age to disease risk.
Nature 488: 471-475.
Mathews, S. and E. M. Kramer. 2012. The evolution
of reproductive structures in seed plants:
a re-examination based on insights from
developmental genetics. New Phytologist 194:
910-923.
Owens, S. A. et al. 1995. Architecture of cauliflory in
the genus Cercis (Fahaceae : Caesalpinioideae).
Canadian Journal of Botany 73:1270-1282.
Potts, D. M. and W. T. W. Potts. 1995. Queen Victoria’s
Gene: Haemophilia and the Royal Family. Alan
Sutton Publishing, Stroud.
Rehder, A. 1907. Einige neuere oder seltenere Geholze.
Mitteilungen der Deutschen dendrologischen
gesellschaft, 1-9.
Rehder, A. 1910. Note on the forms of Kalmia Latifolia.
Rhodora 12: 1-3.
Robertson, K. R. 1976. Cercis: The redbuds. Arnoldia
36(2): 37-49.
Stone, G. E. 1909. A remarkable form of Kalmia latifolia.
Rhodora 11: 199-200.
William (Ned) Friedman is Director of the Arnold
Arboretum and Arnold Professor of Organismic and
Evolutionary Biology, Harvard University.
MAP COURTESY OF WAKDMAPS LLC, CAMBRIDGE, MA. WWW.WARDMAPS.COM
Rediscovering Rhododendron Dell, Part 2
Kyle Port
"They [hoodlums] deliberately twist off the metal labels from trees and shrubs, so
that valuable information is sometimes lost forever and the yearly replacement bill
is terrific. They break hundreds of unopened flower buds off the Rhododendrons
in the early spring."
—Edgar Anderson, Arnold Arboretum arborist , June 4, 1932
Planted in close proximity to one another, Rhododendron 'Old Port’ 990-56-B (a catawbiense hybrid with "vinous crimson"
flowers, seen here) was incorrectly labeled as R. 'Red Head' 329-91-A (with "orient red” flowers). A description published by the
Royal Horticultural Society was used to verify the only remaining plant as 'Old Port'; a lack of indumentum on the undersides
of the leaves distinguishes it from 'Red Head'.
The Arboretum's plant records attest to
episodes of vandalism, arson, theft, and
other willful shenanigans that have
occurred in the living collections over the years.
In 2010, a pile of plant record labels was found
in Rhododendron Dell. This intentional — and
completely unsanctioned — removal of labels
from numerous specimens by an anonymous
person(s) can certainly be considered a major
transgression. But, to quote Albert Einstein, "In
the middle of difficulty lies opportunity," and
this act of vandalism initiated an unplanned
curatorial review that has advanced our under-
standing of the rhododendron collection and
further fostered its use.
In response to the identity crises in Rhodo-
dendron Dell, a multi-year collection review
was conceived. Identity verification and field
work (e.g., labeling, photographing) was timed
to coincide with peak flowering. Winter months
were dedicated to auditing and digesting the
raft of secondary documentation (e.g., records,
articles, herbarium specimens, images) amassed
over the collection's 141 -year history. Through
ALL IMAGES BY THE AUTHOR UNLESS OTHERWISE INDICATED
16 Arnoldia71/l • August 2013
each of these periods, real-time observations
about the collection were recorded in curatorial
databases.
The initial assessment of the collection was
sobering. Many labels were missing and others
had been haphazardly rehung by non-Arbore-
tum staff. Since it was the dead of winter when
the errant labels were found, the rhododendron
flowers — the hallmark structures used to verify
these cultivars — were months away from open-
ing. Partial identities were confirmed using the
leaf characteristics of a few scattered lepidote
rhododendrons and some elepidotes with indu-
mentum. But without flowers, determinations
and label hanging had to wait until spring.
FLOWERING FACILITATES FIELD WORK
Imaging
The window of opportunity to study flowers
in Rhododendron Dell is finite. Depending on
weather conditions, flowers can remain for days
or wither soon after opening. To overcome the
challenges of flower senescence, we used digital
cameras to capture thousands of new diagnostic
images over the past three years. This provided
the first comprehensive image archive of the
collection. Paired with in-field observations,
the images have helped us positively identify
specimens and will eventually become a valu-
able online resource. We will continue to add
rhododendron images to the archive over time.
Inventory field checks
Persistent field observations render the best
results. Over the past three growing seasons,
detailed observations of Rhododendron Dell
plants have been catalogued in curatorial data-
bases. Prior to these efforts, the last major cura-
torial review was undertaken in 1990. Regular,
systematic review of collections and their sec-
ondary documentation (e.g., maps) will likely
reduce the need for time-consuming curatorial
inputs in the future.
Lepidopteran on
an Elepidote
FOR IDENTIFICATION purposes,
rhododendrons can be divided
into two broad groups, lepidotes
and elepidotes. Lepidote rhodo-
dendrons have small scales on
the undersides of their leaves
("lepid" is the Greek root word for
"scale"). They also typically have
small leaves and grow as small
shrubs. Elepidote rhododendrons
do not have leaf scales, usually
have large leaves, and grow quite
large. Some elepidotes have
indumentum (dense, felted hairs)
on the leaf undersides; color and
density of the indumentum can
be a key to identification.
Seen here, an eastern tiger swallowtail butterfly (Papilio glaucus) rests on an elepidote rho-
dodendron. Butterflies and moths are in the insect order Lepidoptera, which references the tiny
scales that cover their wings (and bodies).
Rhododendron Dell, Part 2 17
Labeling
Following the imaging and field checks, hun-
dreds of new anodized aluminum records labels
were embossed and placed in Rhododendron
Dell. Many are mounted on three-inch stain-
less steel screws at the base of large stems.
Additional records labels have been hung on
branches for easy retrieval. In addition to these,
prototypes of larger photo-anodized aluminum
display labels were tested over the peak flower-
ing periods. Feedback regarding these labels has
been overwhelming positive and the roll-out of
permanent signage is expected in 2014.
Mapping
The current maps of Rhododendron Dell are
being revised. Vector data (e.g., points, lines,
and polygons) representing plants and hard-
scape features are being re-collected using
global posistioning system (GPS) equipment.
These technologies allow for decimeter-accu-
rate field mapping and update the triangulation
and submeter-accurate data collection of the
past. Note that interactive maps of Arboretum
collections are available at http://arboretum.
harvard.edu/plants/collection-researcher/
WINTER AUDITS AND RECORDS REVIEW
Nomenclatural review
In advance of label production, we undertook a
comprehensive review of rhododendron nomen-
clature. A total of 103 cultivar names were
standardized following The International Rho-
dodemon Register and Checklist (Royal Hor-
ticultural Society 2004). This effort revealed
inaccuracies in spelling, punctuation, and use
of synonymy for 20 elepidote cultivars. In addi-
tion to these edits, the name records in BG-
BASE (collections management software) were
appended with hybridizer, introducer, parent-
age, awards, descriptions, and common name
as found in the aforementioned resource. We
have used this information to create new dis-
play labels and have updated online resources.
Archival maps and records
The first maps documenting the location of
accessioned plants in the permanent collections
were purportedly authored by Henry Sargent
Codman in 1887. Plan views of the landscape
The gorgeous cultivar 'Brookville' was introduced in
1959 by the Westbury Rose Company based in Long
Island, New York.
On larger specimens, new record labels have been
attached to lower trunks with screws.
ARNOLD ARBORETUM
18 ArnoldiaJl/l • August 2013
This specimen of R. 'Purpuream Elegans', accession
6135-B, came to the Arboretum in 1891 from the nurs-
ery of Anthony Waterer, who hybridized this and many
other rhododendron cultivars.
from this era were copied from the Frederick
Law Olmsted papers in 1987 but as yet do not
reveal individual planting sites. Fortunately,
the detailed cartography begun by Leon Croizat
in the 1930s is well preserved in the Arboretum
archives. Croizat, employing a triangulation
survey method, made his cartographic repre-
sentations of features (e.g., plants, hardscape)
on 24- by 36-inch tracing cloth. Iterations of
these drawings were annotated based on the
field work of Heman Howard and a few others.
The last notations on hand-drawn maps cover-
ing the two acre Rhododendron Dell area are
from the 1980s and 1990s. A total of 90 maps
at scales of 1 inch=10 feet and 1 inch=20 feet
masterfully convey the scope of these collec-
tions over a roughly fifty year period. Since
1987, map edits have been accomplished digi-
tally using AutoCAD (from 1987 to 2008) and
ArcGIS (since 2009) software.
Hand-drawn and annotated paper maps like this one have been replaced with accessible digital files.
»-»><
r’'
Rhododendron Dell, Part 2 19
Rhododendron flower color is often lost in herbarium specimens; compare the 1936 specimen of 'Melton' (left) to a
current digital image of its flowers (right).
In 2010, grant funds awarded through the
Museums for America program of the Institute
of Museum and Library Services (IMLS-MFA)
allowed Jonathan Damery, then a curatorial
assistant, to scan and georeference the collec-
tion of hand-drawn maps. Using ArcGIS soft-
ware, these rasters can he layered with current
representations of the Arboretum grounds. In
addition, they can easily be printed on 11- by
17-inch paper for problem solving in the field.
The IMLS-MFA grant also provided resources to
enter the Arboretum's entire plant records card
catalogue and review accession books (dating
from 1872 to 1987). Spearheaded by curatorial
assistant Kathryn Richardson, the entry of these
data has improved all aspects of curatorial work.
Herbarium resources
A curatorial review would not be complete
without a thorough review of specimens in
the Arboretum's Cultivated Herbarium. In the
case of hybrid rhododendron, these resources
are limited for one major reason: flower color.
Often lost in the drying process, flower color
variations (including the blotch on the dorsal
lobe) are critical identification characters of
rhododendron hybrids. Other flower data such
as truss height, width, shape, fragrance, and
number of buds can be difficult to discern (or be
entirely absent) from a two-dimensional dried
specimen. Without question, examination of
the whole plant at relevant phenophases pro-
vides a more accurate determination.
The importance of identifying rhododendron
flower color accurately is well documented.
Arboretum horticulturist Donald Wyman was
a proponent of the Nickerson Color Fan pub-
lished by the American Horticultural Society
and used this resource to describe the flowers of
Rhododendron Dell collections (Wyman 1969).
Agents of the Royal Horticultural Society,
United Kingdom, have also published a color
chart, which many have used to describe rhodo-
dendron cultivars (Leslie 2004). These color des-
ignations have been saved to the Arboretum's
plant records database and are easily retrieved.
20 Ainoldia71/l • August 2013
A LOOK AHEAD
Collections development
The Arboretum's curatorial staff is ana-
lyzing the current inventory of ever-
green hybrid rhododendrons and will
determine which new cultivars will
be acquired. In the meantime, antici-
pation grows around rhododendron
hybrids already being raised by Dana
Greenhouse staff. Of these, R. 'Robert
Stuart' will likely be sited in Rhodo-
dendron Dell next year. Registered
with the Royal Horticultural Society
in 2006 by long-time Dana Greenhouse
volunteer George Hibben in collabora-
tion with the Massachusetts Chapter of
the American Rhododendron Society,
R. 'Robert Stuart' is an early flowering
lepidote with R. minus and R. concin-
imm in its parentage. Hybridized by the
late Robert Stuart of Stratham, New
Hampshire, unrooted cuttings were
obtained from Gus Mehlquist's garden
by Arboretum propagator Jack Alexan-
der in 1978. The resulting plants were
sited in the permanent collections and
propagated for distribution through the
1989 Arboretum Plant Sale. By 1991,
the Arboretum's specimens had died
but George Hibben's plant thrived. It
is from Hibben's plant that repatria-
tion by way of cuttings of this cultivar
is made possible. Our detailed record
keeping and relationships with like-minded
plantspeople ensure important germplasm is
conserved. R. 'Robert Stuart', with its purple
hued flowers, fading to pink, has been missed
in the permanent collection and its return will
be welcomed.
Beyond historical cultivars, the core collec-
tions of large-leaved Rhododendron species
are under continuous development. In 2006,
wild collected seeds of R. catawbiense and R.
maximum were obtained from Mount Holy-
oke College Botanic Garden in South Hadley,
Massachusetts. Cultivated under a lath house
added to the Dana Greenhouse in 2007, these T.
E. Clark collections from North Carolina were
added to the permanent collections in 2012.
This specimen of R. fortune! (accession 1-2008-A) with a lineage from
west of Tien Mu Shan Reserve in China was planted in Rhododendron
Dell this spring.
More recently, a lineage of Peter Del Tredici's
1989 collection of R. fortunei from west of Tien
Mu Shan Reserve, Zhejiang, China, was added
to the collection this spring.
Infrastructure and horticultural care
In Rhododendron Dell, scouring by Bussey
Brook has compromised the root zones of R.
'Purpureum Elegans', 'Coriaceum', 'Caroline',
and 'Francesca'. Repropagation efforts to con-
serve these accessions are underway by Dana
Greenhouse staff. At the same time, collections
managers are considering options that would
slow the flow of Bussey Brook upstream and
shore up existing infrastructure installed to
mitigate bank erosion through Rhododendron
Other Notable Rhododendron Dells
The Arnold Arboretum's Rhododendron Dell is modest when compared to the largest rhododen-
dron collections of the same name found on earth.
• Dunedin Botanic Garden is New Zealand's oldest botanic garden. Celebrating its
150th anniversary in 2013, its nearly 3,500 rhododendrons are displayed across
10 acres (4 hectares). Dunedin's Rhododendron Dell specimens flower during the
month of October.
• Royal Botanic Gardens, Kew, United Kingdom, maintains a Rhododendron Deli
dating to 1734. It contains more than 700 rhododendron specimens and reaches
peak flowering in April and May.
• Conceived in 1942, Golden Gate Park's John McLaren Memorial Rhododendron
Dell in San Francisco, California, has been under extensive renovation since 2001.
Between April and May, an estimated 850 rhododendron hybrids flower.
Arboretum horticulturist Brendan McCarthy and Hunnewell interns
John Aloian and Ryan Plante at work in Rhododendron Dell, May 2012.
Dell. Previous efforts in this regard were
completed for the western section (in
1990) and eastern sections (in 1995) of
Bussey Brook. With some repairs over
20 years old, an undertaking of similar
scope is needed.
Arboretum horticulturists put much
effort into maintaining the Rhododen-
dron Dell collections. Annual removal
of bud blast, a fungal disease that ruins
flower buds, has greatly reduced its
incidence. Damage from root weevils
(chewed leaves) and stem borers (dead
branches) is being monitored and control
methods are being investigated. Exten-
sive deadwood removal by horticulturist
Sue Pfeiffer in the fall of 2012 has encour-
aged new stems to regenerate from the
base of many historical cultivars. This
new growth is encouraging, since some
of the finest specimens in the collections
currently hold their flowers well above
the heads of their admirers. In addition
to maintenance pruning, the separa-
tion of abutting accessions by removing
tangled layers is underway. This step is
critical and will undoubtedly help pre-
vent identity confusion going forward.
Attention has also turned to the
overstory. The application of imidaclo-
prid (insecticide) has saved some of the
surrounding eastern hemlocks {Tsuga
22 Ainoldia 7 1 / 1 • August 2013
canadensis] from the voracious appetites of
hemlock woolly adelgid (HWA), but we con-
tinue to research which tree species should be
planted to succeed old-growth hemlocks. To
prevent excessive competition, it is likely that
a number of oak [Quercus], mountain ash (Sor-
bus], beech [Fagus], and linden [Tilia] accessions
will be removed or transplanted from Rhodo-
dendron Dell in the coming year.
HYBRIDIZATION
Hybridization in Rhododendron can occur nat-
urally and frequently between sympatric spe-
cies (Milne et al. 1999), but it takes the hands of
plant hybridizers to bring together wild and cul-
tivated Rhododendron from around the globe.
When successful, these intentional unions
result in exciting new crosses. The Rhododen-
dron Dell collections reveal the masterful tal-
ents of many hybridizers through the years. The
earliest and latest documented hybridization
efforts in the Arboretum's collection are seen in
R. 'Cunningham's White' (introduced by James
Rhododendron ‘Cunningham's White' was introduced
around 1830 by James Cunningham of Edinburgh,
Scotland, and has been widely used in hybridizing.
Cunningham in 1830) and R. 'Landmark' (from
Wayne Mezitt inl985).
The specimens in Rhododendron Dell come
from over 65 sources, including nurseries, hob-
byists, and other botanical institutions. The
highest numbers of accessions were acquired
from Waterer (Bagshot and Knap Hill), Van Veen
Nursery, Westbury Rose Company, and agents
of the American Rhododendron Society, Massa-
chusetts Chapter. There are extensive personal
and institutional legacies tied to each specimen
in Rhododendron Dell.
Parentage
Tens of thousands of Rhododendron cultivars
have been formally registered under the aus-
pices of the Royal Horticultural Society. Of
these, the Arnold Arboretum grows a mere frac-
tion. At least one or all of the parent species of
Rhododendron Dell cultivars are known. Eigh-
teen cultivars (17% of total) are of unknown
parentage or probable parentage is cited; these
are excluded from Table 1.
A catawbiense hybrid from E. V. Mezitt, Weston Nurser-
ies, Rhododendron 'Henry's Red' is a relatively young
cultivar (selected around 1970, registered in 1987) noted
for its deep red flowers and excellent cold hardiness.
Table 1. Arnold Arboretum: The Parent Species of Rhododendron Dell (RD)
Cultivars as of January, 2013
SUBSECTION
SPECIES
TRAITS VALUED BY
HYBRIDIZERS
NATIVITY
% of total (RD)
cultivars (n = 103)
with known parent
(backcrosses not tallied)
Fortunea
R. griffithianum
Large flowers (some of
the largest of the genus)
E. Nepal, Sikkim,
Bhutan, N.E. India
3% (n = 4)
Fortunea
R. fortune!
Scented flowers;
heat resistant
Most widely distributed
Chinese species.
7% (n=8)
Pontica
R. catawbiense
Extreme hardiness;
tolerant of exposed
sunny sites
E. United States; South-
eastern Appalachian
Mountains
48% (n = 50)
Pontica
R. caucasicum
Tolerant of poor,
dry soil
N.E. Turkey and parts
of the Caucasus
2% (n - 3)
Pontica
R. macrophyllum
Flowers often with
crinkled lobes, rachis
fairly tall
W. North America
<1% (n = 1)
Pontica
R. maximum
Large, narrow, dark
green leaves
E. North America
5% (n = 6)
Pontica
R. ponticum
Species commonly used
as understock
Caucasus and
N. Turkey
5% (n = 6)
Pontica
R. smirnowii
Hardiness;
thick indumentum
N.E. Turkey and
Caucasus
2% (n = 3)
Rhodorastra
R. dauricum
Hardiness;
early flowering
E. Russia, Siberia,
Mongolia, N. China,
Japan
1% (n = 2)
Rhodorastra
R. mucronulatum
Hardiness;
early flowering
E. Siberia, China, Mon-
golia, Korea, Japan
2% (n = 3)
Neriiflora
R. haematodes
Small stature; longevity
of leaf retention
China: W. and
N.W. Yunnan
<1% (n= 1)
Pentanthera
R. prinophyllum
Hardiness
E. North America
<1% (n = 1)
Scabtifolia
R. racemosum
Tolerant of dry soils
China
1% (n = 2)
Arborea
R. arboreum ssp.
arboreum
Leaf, silvery indumen-
tum; flower bright red
to carmine, rarely pink
or white
Himalayan foothills,
Kashmir to Bhutan
2% (n = 3, two are
R. arboreum)
Arborea
R. arboreum ssp.
cinnamomeum
var. roseum
(Album Group)
Leaf, rusty brown
indumentum; flower
with purple spotting
in throat
E. Nepal, N.E. India,
Bhutan, S. Tibet
<1% (n = 1)
Maddenia
R. ciliatum
Hardiness (variable)
E. Nepal, Sikkim,
Bhutan, S. Tibet
1% (n = 2)
Additional hybrids of interest grown in Rhododendron Dell include:
R. X myrtifolmm {R. Mrsutum x R. minus); R. hirsutum tolerates near-alkaline soils and is native to the European Alps
R. X laetevirens {R. minus x R. ferrugineum); R. ferrugineum does not flower in abundance but is hardy and late flowering.
24 Arnoldia 71/1 • August 2013
Rhododendron 'Catawbiense Album' is a hardy hybrid introduced by Anthony Waterer in 1886.
Rhododendron Dell, Part 2 25
Native to the Caucasus Mountains, R. smirnowii is the hardiest indumented
rhododendron species. Its distinctive indumentum and crinkled petal edges
are traits favored by hybridizers.
References
Cox, P. A. and K. N. E. Cox. 1997. The Encyclopedia of Rhododendron Species. Perth, Scotland: Glendoick Publishing.
Leet, J. 1990. The Hunnewell Pinetum: A Long Standing Family Tradition. Arnoldia 50(4): 32-40.
Leslie, A. C. 2004. The International Rhododendron Register and Checklist, second edition. London: Royal
Horticultural Society.
Madsen, K. 2000. In pursuit of ironclads. Arnoldia 60(1): 30-32.
Milne R. I., R. J. Abbott, K. Wolff, and D. F. Chamberlain. 1999. Hybridization among sympatric species of
Rhododendron: (Ericaceae) in Turkey: morphological and molecular evidence. American Journal of Botany
86: 1776-1785.
Nilsen, E. T. 1990. Why do rhododendron leaves curl? Arnoldia 50(1): 30-35.
Rieseberg, L. H.and S. C. Carney. 1998. Plant hybridization. New Phytologist 140: 599-624.
Sargent, C. S. 1914. Rhododendrons. Bulletin of Popular Information no. 57, June 5, 1914.
Wilson, M. J. 2006. Benjamin Bussey, Woodland Hill, and the Creation of the Arnold Arboretum. Arnoldia 64(1): 2-9.
Wyman, D. 1969. Seventy-five years of growing rhododendrons in the Arnold Arboretum. Arnoldia 29(6): 33-40.
Kyle Port is Manager of Plant Records at the Arnold Arboretum.
The World of Mosses
Stephanie Stuber
W
hile the more charis-
matic trees and flashy
flowers initially catch
our attention, mosses have an
enchanting, charming presence.
What is it about these tiny plants
that intrigue us? Perhaps we are
aware that there is so much more
to their story, but their secrets
remain intangible, concealed by
their diminutive size.
Mosses differ from other plants
largely in their life cycle. Mosses
and tracheophytes (traditionally
known as vascular plants) both
alternate between two conditions
throughout their lives, the gameto-
phyte and sporophyte. The gameto-
phyte is haploid (n), having 1 set of
chromosomes, and the sporophyte,
being the product of fertilization,
is diploid (2n) with 2 sets of chro-
mosomes. Tracheophytes conceal
their gametophytes in reproduc-
tive structures, like flowers, never
to be seen while they develop
into the gametes (sperm and egg).
For tracheophytes, the dominant
condition is the sporophyte — the
woody or herbaceous plant itself.
The sporophyte produces spores
that remain hidden when they
develop into the gametophytes
which then develop into the gam-
etes. In essence, the gametophytes
are dependent on the sporophyte.
But in mosses, the sporophyte
is dependent on the gametophyte. The dom-
inant condition is reversed; the conspicuous
green leafy plant is the gametophyte, and the
sporophyte is an ephemeral structure produced
seasonally. The roles are the same, though —
Mosses carpet the forest floor at the Coastal Maine Botanical Gardens.
gametophytes produce gametes and the sporo-
phyte produces spores. The spores, however, are
released into the air before they develop into
the gametophyte, rather than remaining hidden
in reproductive structures.
Mosses 27
SEXUAL REPRODUCTION IN MOSSES
1 . A leafy female gametophyte fn) with attached terminal sporophyte (2n).
2= A papery protective covering, the calyptra (n), sheds off when the capsule {2n) fully develops,’ a remnant of the interior
archegonial wall. Spores develop by meiosis inside the capsule.
3. A cap, the operculum (In], pops off the capsule when spores are mature.
4. A row of tiny teeth, the peristome (In), aids in spore dispersal
5. A spore in] settles ©n a place to germinate.
6. The protonema {nj emerges from the spore, reminiscent of filamentous algae, and develops into mature male and/or
female plants depending on the species.
7. A cluster of antheridia (n) develop on the male.
8. A cluster of archegonia (n) develop on the female.
9. In the presence of water, flagellate sperm in) are released from the antheridium and swim to the egg in) in the archego-
rrium to fertilize it.
1 0. The fertilized egg (2n, zygote) develops inside the archegonium and emerges as the sporophyte.
28 Anioldia 71/1 • August 2013
Tetraphis pellucida frequently produces terminal cups holding gemmae (clus-
ters of undifferentiated photosynthetic tissue). With the splash of a raindrop,
the gemmae are dispersed. One gemma will develop into a new moss plant.
Orange sporophytes can also be seen in this photo. This species is very common
on rotting stumps.
Dicranum flagellate is frequently found with filamentous brood branches. These
tiny clusters of branchlets are borne in the leaf axils extending past the leaves,
giving the moss a distinctive texture. These branches will easily break off when
you rub a finger across the surface, as evidenced by the indented area with bro-
ken brood branches. This is a very common woodland species on soil.
capsule
seta
leaves
rhizoid
All mosses possess these basic anatomical
parts (with few exceptions) as displayed by
Polytrichum commune.
When conditions do not favor sexual repro-
duction, mosses can always reproduce vege-
tatively from broken fragments of the plant.
Moss cells are totipotent, which means that
a single, differentiated cell has the ability to
develop into an entire, fully functional plant.
Some species produce propagules specifically
designed to break off with the help of a passing
animal or a raindrop. Above are two examples
of these asexual structures.
A couple of studies were recently published
which introduced the idea that mosses are not
exempt from the animal pollinator association.
The flagellate sperm were thought to require a
film of water to swim to an egg. But this study
has shown water is not necessarily a limiting
factor in fertilization (Cronburg 2006). Appar-
ently springtails and mites can play a signifi-
cant role in moss fertilization, independent of
sufficient water availability. A second study
found that mosses produce pheromone-like
chemicals that actively entice these tiny inver-
tebrates to carry the sperm to an egg (Rosensteil
2012). This profound discovery gives credence
to the theory that mosses may have instigated
the plant-pollinator relationship so prevalent in
Mosses 29
higher plants today. This model may also bridge
the gap between their aquatic algal ancestors
and the terrestrial tracheophytes.
MOSSES UP CLOSE
When you first take a look at a moss plant, with
your naked eye or under a hand lens, often the
first thing you notice are striking similarities
to other plants. Mosses have stems, tiny leaves,
and little rootlike structures. With the aid of a
microscope you may see more parallels: a mid-
rib, a serrated margin, conductive tissues, even
tomentum. These structural analogs have simi-
lar purposes in both mosses and tracheophytes.
Mosses come in an enormous array of shapes,
sizes, forms, colors, and textures, but most are
made up of the same components. Members
of the genus Polytrichum are commonly used
to represent a typical moss species because
of their relatively large size and distinct fea-
tures. The gametophyte consists of parts simi-
lar to most other tracheophytes. The leaves of
mosses are called phyllids to distinguish them
from the true leaves of tracheophytes, which
have lignified vascular tissues, but bryologists
will call them leaves regardless, understanding
their technical differences. These simple leaves
are arranged spirally along the stem. This is a
good distinguishing characteristic from liver-
worts, whose leaves are distichous (arranged
in a two-ranked fashion on opposite sides of
the stem). Instead of roots, mosses have similar
structures called rhizoids. They do not make
up an extensive subterranean network; rather,
they are superficial and act more as a holdfast
to anchor the moss to its substrate. The sporo-
phyte consists of a stalk called a seta and the
capsule, whose main parts are shown in the
lifecycle image.
My undergraduate professor. Dr. Robin Kim-
merer, described mosses as "time made vis-
ible," and mosses undoubtedly do lend a certain
timeless aesthetic to the landscape. Intuitively
we relate the amount of mosses in an area to
the length of time it has remained undisturbed.
What perpetuates their reputation for being
slow growing? Mosses, unlike most life forms
on this planet, are poikilohydric. This means
that they cannot internally regulate water, so
are subject to moisture fluctuations in their
The acrocarpous Ulota hutchinsiae has sporophytes that
emerge terminally from the gametophyte.
The mat-forming pleurocarp Hypnum imponens sends out
sporophytes laterally.
30 Amoldia 7 1 / 1 • August 2013
pendant dendroid weft mat turf cushion
pendant dendroid weft mat turf cushion
< — — — — — — - — — — — >
aquatic mesic xeric
This drawing illustrates the shift in moss morphology based on habitat water availability.
immediate environment; when it is wet, they
are wet, when it is dry, they are dry. Like other
plants, mosses need to have access to water and
light simultaneously to photosynthesize — only
then can they actively grow. They are adept at
capturing light at very low levels, hut not at
holding water, so their window of opportunity
to grow is limited in many natural systems.
Moss leaves are usually only one cell layer
thick. They lack an epidermis and mesophyll
layer, and rarely have a waxy cuticle as found in
true leaves. This is what makes mosses poiki-
lohydric, hut it also gives them great flexibility
in where they can live. Water and nutrients are
acquired primarily through the surface of their
leaves. This also makes them especially sen-
sitive to toxins and other pollutants, making
them ideal environmental indicators. They do
not necessarily depend on their substrate for
their nutritional needs; their rhizoids provide
minimal water and nutrient uptake. The com-
bination of their rhizoids and their thin leaves
allow them to grow superficially on imperme-
able surfaces like rocks and tree trunks.
With little to guard them against their envi-
ronment, mosses are quite vulnerable. They are
always open and receptive to what is offered to
them, to their benefit or detriment. Amazingly,
they can lose up to 98 percent of their water
content and cease their metabolic functions for
a time. Any other organism in this state would
be considered dead, but mosses will revive once
water returns.
Mosses can be divided into two growth
forms — acrocarpous or pleurocarpous — based
on the location of their sporophyte. Acrocarps
bear theirs terminally, while pleurocarps bear
theirs laterally. This is often the initial distinc-
tion used when identifying mosses. Typically
the gametophytes of either form are distinctive
enough, which helps in year-round identifica-
tion if the sporophyte is not present. Acrocarps
are generally upright, rarely branched, and form
turfs and cushions, whereas pleurocarps are
generally prostrate with pinnate, ferny forms.
FORM FOLLOWS FUNCTION
Within these two growth forms, mosses are seg-
regated into many different life forms,- six of the
most common are shown here. One thing about
these life forms that is especially fascinating
is the link between morphology and habitat.
In the diagram above, the forms are arranged
along a water availability gradient ranging from
aquatic to xeric habitats. Clearly morphology
is a function of water availability. Those spe-
cies that grow in fresh water are not limited by
extended dry periods, so their gametophytes are
Mosses 31
filamentous and essentially formless, offering
much of their surface area to the open envi-
ronment. As you move through mesic to drier
habitats, the forms become more complex. The
dendroid forms are still loose, but have rigid
stems to support upright growth on saturated
land. The pinnate forms with more intricate
and rigid designs increase the amount of capil-
lary spaces, helping to conserve water in mesic
areas. Habitats with limited water tend to sup-
port turf and cushion forms best. Their tight,
dense forms and specialized cellular structures
and appendages facilitate water retention in
drier environments.
Their desiccation tolerance is also directly
related to their morphology; those species that
live in wet areas will have less tolerance to des-
iccation than those species that are subjected
to intermittent water availability. Because of
their poikilohydric nature, mosses have had to
develop ways to survive those dry periods in
order to continue colonizing land further away
from a water source.
The length of time that some mosses can
survive without water is remarkable. Aquatic
mosses can remain desiccated for a few months
to as much as a year, mesophytic species can
wait several years without water, and xero-
phytic species are known to survive decades or
centuries without water. Once water returns,
they will begin repairing the cellular dam-
age incurred by the desiccation process and
then begin photosynthesizing once more. Of
course, this is observed along a spectrum. The
trend between form and desiccation tolerance,
though positive, is dependent on the rate of the
desiccation process; the slower the drying rate,
the longer it can survive in that state.
A close-up view of sphagnum moss reveals its rich texture.
32 Arnoldia 71/1 • August 2013
Mosses are able to tolerate colder tempera-
tures than tracheophytes. Some species that live
in harsh winter climates are nearly black when
dry, allowing them to absorb as much light
energy as possible to increase warmth. When
the snow arrives, they lie protected underneath
the icy blanket until it begins to melt. As water
becomes available and even slight amounts
of sunlight penetrate through the snow, the
moss will begin photosynthesizing. Even the
minor amount of nutrients dissolved in melted
snow is enough to sustain them. Their incred-
ible temperature tolerance and low-light-
capturing ability gives them the upper hand
at colonizing the harshest of climates. They
are unique among plants in that they are found
on all seven continents and every ecosystem
except the ocean.
THE WIND IN THE MOSSES
The boundary layer exists as the interface
between any surface and the surrounding air.
At the surface, air is slowed by friction, while
higher up the air is unimpeded. In between is
turbulence. Mosses thrive close to their sub-
strates, where, in the stillness, they can capture
and retain heat, water, nutrients, and gases in
their capillary spaces.
While moss gametophytes are content to
grow within the boundary layer, the sporo-
phytes depend on air movement for spore dis-
persal. Most sporophytes are designed to extend
beyond the boundary layer into the turbulent
zone, elevating the capsules with the seta so
that spores can be released into the wind. The
peristome that surrounds the opening of the
capsule ensures that the spores are released at
optimal times and in an effective way. Spores
travel farther in dry conditions, so the peristome
teeth reflex outward when it is dry, allowing
spores to escape, and retract inward when it is
wet. These teeth also act as a "salt shaker" by
making sure the spores do not clump together
as they are released.
The effects of the boundary layer benefit not
only the moss itself, but the whole ecosystem.
In many respects mosses act like mulch by
absorbing and releasing water slowly and main-
taining humidity in the atmosphere and below
ground. They also help reduce water runoff
and control erosion. As water moves through
a carpet of moss, most of the particulates and
sediment is left behind, leaving clean, filtered
water and keeping the top soil intact (Thieret
1956). Like all plants, mosses sequester carbon
and other nutrients until they are released back
into the environment from leaching
or decay. Interestingly, this sediment
retention is what gives some mosses
the ability to literally build stone.
Beds of moss can form the calcare-
ous limestone known as travertine by
providing a site that accelerates the
evaporation of calcareous water, leav-
ing the minerals underneath behind.
The dissolution of this stone with
acid can reveal tiny moss fragments
as evidence (Thieret 1956).
The complex morphology of xero-
phytic mosses clearly illustrates the
clever ways mosses have arranged
themselves to conserve water. Many
of these species can tolerate a good
amount of sun exposure, so to coun-
teract the subsequent water loss these
species often possess filamentous
apical structures called awns. The
laminar flow
turbulent zone
boundary layer
The movement of air across a bed of moss.
Mosses 33
Polytrichum piliferum gives off a silvery cast with its very long clear awns and thin waxy cuticle that covers the leaves.
awns are often white or greyish, which
is thought to aid in light reflection, thus
cooling the plant and protecting it from
damaging ultraviolet light. These awns
extend beyond the leaf margins, increas-
ing the boundary layer blocking desic-
cating air flow.
Some species have found ways to
thicken their leaves to help retain water
longer. Some can have short protrusions
on the cell surface called papillae. Papil-
lose species have a dull, matte appear-
ance from a distance because of their
roughly shaped cells, as opposed to the
shiny appearance of species with smooth
cells. Members of the Polytrichaceae
have lamellae — multistratose plates of
cells aligned perpendicularly over the
leaf surface, effectively thickening the
The awn of Tortula ruralis.
34 Amoldia 7 1 / 1 • August 2013
Transverse cross section of Polytrichum juniperinum showing the lamel-
lae and the leaf margin folds over them (lOOx).
leaf. Those extra cells and the capillary spaces
between the lamellae hold water as well as add
more surface area for photosynthesis and gas
exchange. Some species will even fold their leaf
margins over the lamellae for added protection
as seen in the image above.
Another way mosses counteract water loss
is by altering their form as they dry out. For
many species, their leaves begin to fold and curl
when cells lose water. This reaction helps trap
and hold any remaining water by creating more
capillary spaces for water to adhere. The uneven
surface created by the contorted leaves also
increases the boundary layer. It is this action
that makes some species look very different in
a hydrated versus desiccated state. The rehydra-
tion process can take less than a minute and is
amazing to watch. The thin leaves will readily
absorb water, and as the cells expand, the tiny
leaves unfurl gracefully.
MOSSES: A WORLDVIEW
A couple of years ago I took a trip to Denver. I
have flown countless times, and I always enjoy
viewing our planet from that altitude. It seemed
during that trip, however, that my perception
of plant life had crossed a new threshold. Over
the years I had trained my eyes to focus on the
patterns of mosses growing in their natural
setting. So, at 32,000 feet, I could not
help but draw the comparison between
moss growth patterns and the patches
of forest below. From that perspective
I noted how trees formed turfs and
tufts across the land, concentrating
along waterways and protected areas.
This is not unlike what we observe
of mosses on the forest floor from our
human perspective. The same natu-
ral, microclimatic forces apply in the
colonization of a forest along land as
it does for mosses along its substrate. I
was reminded of the ancient hermetic
axiom "As above, so below," which
points to the irrelevance of scale; the
same ecological patterns are apparent
throughout all level of natural systems.
On your next encounter, I invite you
to stop and pet the mosses (by doing
so you will be breaking off tiny pieces,
helping it grow vegetatively) and reflect on their
significance, similarities, and strength. They
hold a necessary place in the ecological func-
tion of their environments and, while tiny, they
still share many traits v/ith their tracheophyte
relatives. They model themselves in patterns
congruent with much larger plants to perform
the same processes optimally — that is the rea-
son why some mosses resemble little conifer
seedlings! Mosses reflect that which we already
see and know of our natural world and while
they can help us reflect on the importance of
being open and accepting and having patience
and faith, they will continue to enrich us with
their concealed secrets and attractive aesthetic.
Citations
Cronberg N., R. Natcheva, and K. Hedlund. 2006.
Microarthropods mediate sperm transfer in
mosses. Science 313: 1255.
Rosenstiel, T. N., E. E. Shortlidge, A. N. Melnychenko, J.
F. Pankow, and S. M. Eppley. 2012. Sex-specific
volatile compounds influence microarthropod-
mediated fertilization of moss. Nature. 489:
431-433.
Thieret, John W. 1956. Bryophytes as Economic Plants.
Economic Botany 10; 75-91.
References
Crum, H. A. 2004. Mosses of the Great Lakes Forest.
Ann Arbor, Michigan; University of Michigan
Herbarium.
Mosses 35
A moss microcosm composed of star-shaped Polytrichum commune, windswept
Dicranum scoparium, and short, pale Leucobryum glaucum.
Crum, H. A. and L. E. Anderson. 1981. Mosses of Eastern
North America. 2 vols. New York; Columbia
University Press.
dime, J. 2007. Bryophyte Ecology. 5 vols. Ebook sponsored
by Michigan Technological University and the
International Association of Bryologists. Accessed
in 2013 at http://www.bryoecol.mtu.edu
Goffinet, B. and A. J. Shaw. 2009. Bryophyte Biology.
2nd Edition. Cambridge, United Kingdom;
Cambridge University Press.
Kimmerer, R. W. 2003. Gathering Moss: A Natural and
Cultural History of Mosses. Corvallis, Oregon:
Oregon State University Press.
Malcolm, W. and N. Malcolm. 2006. Mosses and Other
Bryophytes: An Illustrated Glossary. Nelson,
New Zealand: Micro-Optics Press.
Stephanie Stuber is a former Arnold Arboretum Curatorial
Fellow and author of The Secret Lives of Mosses: A
Comprehensive Guide for Gardens.
Chamaecyparis obtusa 'Chabo-hiba' 877-37
A Venerable Survivor
Peter Del Tredici
When people ask "What's the oldest tree
growing at the Arnold Arboretum?"
they're usually surprised to learn that
it's a 276-year-old compact hinoki cypress
[Chamaecyparis obtusa 'Chabo-hiba', accession
877-37) that stands only four feet tall. It is one of
seven 'Chabo-hiba' specimens in the Larz Ander-
son Bonsai Collection that were imported from
Yokohama, Japan in 1913. This makes 2013 a
milestone for the tree — the hundredth anniver-
sary of its arrival (and survival) in North Amer-
ica. It makes my head spin to think that someone
has been watering this plant pretty much every
day since well before the American Revolution!
While this 'Chabo-hiba' is not the oldest Japa-
nese bonsai in the United States (there are older
ones at the United States National Arboretum
in Washington, D.C.) the Arboretum's plant has
been under continuous cultivation longer than
any other bonsai growing in North America.
Larz Anderson attended Harvard College (class
of 1888) and later served as a diplomat in the
Foreign Service. In 1912, near the end of the Taft
administration, he was appointed "Ambassador
extraordinary" to Japan, a post he held for only
six months, until Woodrow Wilson moved into
the White House. During his brief stay, Ander-
son was smitten by the "bonsai bug," and in
early 1913, shortly before completing his post-
ing, he purchased at least forty plants from the
Yokohama Nursery Company to bring back to
his estate in Brookline, Massachusetts. Many
of the specimens offered for sale by the nursery
were already hundreds of years old. Photographs
from the time show that the 'Chabo-Hiba'
plants were often trained into a conical shape —
suggestive of a distant mountain — with regularly
arranged, horizontal branches.
Anderson and his wife Isabel (Weld) left Japan on
March 6, 1913, and it seems likely that the plants
followed them across the ocean in a shipment
that autumn. Once they arrived, the trees were
displayed on the terraces of the Anderson home
where they resided for nearly twenty-five years.
The collection was donated to the Arbore-
tum in two batches, initially in 1937 follow-
ing Larz's death, and later in 1948, following
Isabel's death. 'Chabo-hiba' 877-37 came to the
Arboretum in the first installment and was put
on display along with the other plants in a lath-
house on the grounds of the former Bussey Insti-
tution. They remained there until 1962 when
they moved into their current hexagonal home
near the Dana Greenhouses.
In 1969 the Arboretum appointed Connie
Derderian to take care of the plants. As hon-
orary curator, Connie revitalized the collec-
tion after years of neglect and took care of the
plants until 1984. Having worked as Connie's
apprentice since 1979, 1 became the new curator
the year she retired. In 1998, the noted English
bonsai master, Colin Lewis, became involved
with the collection.
The fact that seven large 'Chabo-hibas' have
survived the ravages of both time and occasional
neglect for the past hundred years is a testament
to the incredible durability of the plants them-
selves. By virtue of their longevity, the plants
provide a direct link not only to the early 1900s,
when wealthy Americans were passionately col-
lecting cultural artifacts from Asia, but also to
the Tokugawa era in Japan (1600 to 1868) when
shoguns ruled the land and the plants themselves
occupied places of honor in temples throughout
the country.
The hinoki cypress cultivar name chabo-hiba
is not widely used in Japan today, and it took
some effort to uncover its history and mean-
ing. The word hiba is the common name for
the arborvitae-like conifer Thujopsis dolobrata
and means "hatchet-shaped," in reference to the
scale-like foliage of the plant. Chabo means ban-
tam or dwarf chicken, and when combined with
hiba means "compact or dwarf cypress." In the
landscape, Chamaecyparis obtusa 'Chabo-hiba'
is a relatively slow-growing plant that develops
a pyramidal shape when left unpruned. When
grown in a container and intensively pruned, it
produces congested, planar foliage and contorted
horizontal branches, resulting in striking bonsai
specimens like accession 877-37.
Peter Del Tredici is a Senior Research Scientist at the
Arnold Arboretum.
Selected specimens from the Larz Anderson Bonsai Collection will be on display at the Isabella
Stewart Gardner Museum in Boston from October ind to ijth, 2013.
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