a(Oleaceae). Phytoneuron 2010-37: 1-9. Mailed 1 September

TAXONOMIC STATUS OF FRAXINUS CORIACEA (OLEACEAE)

GuyL. Nesom

2925 Hartwood Drive

Fort Worth, TX 76109, USA

www.guynesom.com

ABSTRACT

Fraxinus coriacea has been treated as a variety of F. latifolia ( :=; F. oregona) and of F.
velutina. Its geographic range is essentially intermediate (in southern California, Nevada,
southwestern Utah, northwestern Arizona) between the two others. Intermediates apparently occur
with each of the latter but F. coriacea can be recognized as a distinct entity on the basis of its
morphology and geography and each is treated here at specific rank. Maps show the county-level
distribution for each of the three and the detailed distributions of F. latifolia and F. coriacea. A
lectotype is designated for F. oregona var. glabra.
KEY WORDS: Fraxinus coriacea. F. velutina, F. latifolia, taxonomy

Trees identified as Fraxinus coriacea S. Wats. (1873) from the southwestern USA have had
an inconsistent taxonomic history. Sargent (1894) included F. coriacea in the synonymy of F.
velutina but later (1902, p. 33) treated it as a distinct species and included Faxon's line drawing of it
(reproduced here as Fig. 1). "In the sixth volume of this work [Silva of North America] Fraxinus
coriacea was considered a form of Fraxinus velutina. It differs from that species in its fewer longer-
stalked leaflets which are more coriaceous and more coarsely serrate, and in its range, Fraxinus
coriacea being a tree of the mesas and low plains, while Fraxinus velutina is an inhabitant of
mountain canons; and with our still slight knowledge of the southwestern species of Fraxinus it is
perhaps best to consider it a species." Still later, Sargent (1922) treated the southern California trees
as F. oregona var. glabra, not recognizing F. coriacea even as a synonym: "the var. glabra in Los
Angeles and San Bernadino Counties, and east of the Sierra Nevada in Inyo County (Ash Creek near
Owens Lake), and occasionally northward in California."

Rehder (1917) apparently was the first to formally associate Fraxinus coriacea with F.
velutina, treating it as F. velutina var. coriacea (S. Wats.) Rehder. Munz and Laudermilk (1949)
observed that var. coriacea "is a recognizable variety of F. velutina with enough characters and
distinct range, F. velutina itself not being known from California." They also (1949, p. 60) noted that
"Rehder's F. oregona var, glabra, on the basis of plants so identified and of characters used and range
given, seems to be a synonym of F. velutina var. coriacea as treated by Jepson (Fl. Calif. 3: 80,
1939)." Fraxinus velutina var, coriacea has been recognized by Lingelsheim (1920), Jepson (1939),
Abrams (1951), Munz and Keck (1959). Shreve and Wiggins (1964), and Wiggins (1980).

Miller (1955) treated both Fraxinus velutina and F. latifolia as subspecies within her
extremely broad concept of Fraxinus pennsylvanica and recognized F. coriacea simply as a synonym
of F. velutina. Holmgren (1984) also included/ 7 , coriacea simply as a synonym of F. velutina, as did
Wilken (1993), who recognized F. velutina as widely distributed in southern California and noted that
it apparently hybridizes with F. latifolia. Wallander (2008) did not consider F. coriacea even as a
synonym.

Among those who have recognized Fraxinus coriacea as a distinct entity, descriptions of its
diagnostic features have been relatively consistent, and the present study also is in agreement. These
trees are characterized by thick leaves, usually glossy above, typically broadly obovate and distally

Nesom: Taxonomic status of Fraxinus c

serrate, often with minutely apiculate teeth. The lateral veins are prominent and slightly raised, 6-9(-
13) on each side, arching upward, conspicuously parallel and running nearly to the margin before
branching. A raised reticulum of smaller veins is prominent on both surfaces. The minute peltate
scales on the leaflet abaxial surfaces appear to be slightly sunken into the epidermal surface. As
noted by Munz and Laudermilk (1949) leaf vestiture varies from glabrous to hirtellous on both
surfaces. They also found that F. coriacea differs from F. lattfolia in microsculpturing of the abaxial
leaflet surfaces — it differs in microsculpturing from F. velutina as well but less so than from F.
lattfolia.

Munz and Laudermilk (1949) noted that intermediates occur between Fraxinus coriacea and
F. lattfolia. especially in Tulare County, at the northern end of the range of F. coriacea and,
according to them, at the southern extremity of F. lattfolia. Owston's map (1990; reproduced as Fig.
5 in the present study) showed F. lattfolia reaching slightly further south into northern Kern County,
and Little (1971) mapped F. lattfolia with a disjunct southern segment reaching through Ventura, Los
Angeles, and San Bernadino counties.

Observations in the present study also indicate that Fraxinus lattfolia sensu stricto reaches the
southern counties of California, although uncommon there, where it may account for some of the
variability in F. coriacea. The distinctive, stiffly curving, partially reclining foliar hairs (abaxial
surfaces) of F. lattfolia never occur in F. coriacea but are abudantiy produced by plants of the
following collections. Los Angeles Co.: La Tuna Canyon, Verdugo Hills, sandy wash, 26 Mar 1933,
MacF s.n. (NY). Riverside Co.: southern Santa Ana Mts., San Mateo Canyon Wilderness Area,
along San Mateo Creek from Riverside Co. line, following San Mateo Trail upstream to confluence
with Bluewater Canyon, riparian, 800-100 ft, 23 Apr 1992, Boyd 7068 (NY). San Diego Co.: Hot
Springs, Jun 1880. Vasey 365 (NY); Cleveland Natl. Forest, Trabuco District Rd 7504 at jet with
Alamos Canyon Creek, riparian habitat in chaparral, 200 m, 8 Mar 1995, Walker 1236 (NY); along
Cottonwood Creek, 2.3 mi above Barrett Store, on road to Barrett Dam, 1100 ft, 28 Oct 1940, C.B.
Woltfs.n. (TEX; this specimen from a cultivated tree in RSA Botanic Garden, grown from the original
collection by Wolf).

In summary and conclusion, Fraxinus coriacea has been onsi tf-nth recognized is a distinct
entity in studies with a broader purview, although it has sometimes been treated as an element within
F. velutina. The current study further confirms its apparent morphological and geographical reality.
In view of its discrete geographical range and intermediate position between F. velutina and F.
lattfolia, hybridization and intermediacy between these two and F. coriacea probably is less common
than previously suspected. In fact, given its allopatric distribution. F. coriacea seems relatively
simply to identify and treatment at specific rank appears to be justified.

Fraxinus coriacea and F. lattfolia can be distinguished by the following contrasts.

1. Leaflets relatively thick, venation distinctly raised on both surfaces, blades mostly obovate,
glabrous or hirtellous with straight erect hairs, margins toothed on distal 1/2-1/3 to entire; lateral

petiolules 5— 10(— 13) mm Fraxinus coriacea

1. Leaflets relatively thin to thickened, venation not raised, blades mostly oblong elliptic-oblong to
oblong-ovate or oblong-obovate, sparsely to densely villous abaxially with stiffly curving, reclining
hairs, margins usually entire; lateral petiolules 0(-3) mm Fraxinus latifolia

Intermediates also apparently occur between Fraxinus coriacea and F. velutina, especially in
southwestern Utah in the restricted region where there ranges apparently come into contact. Other
plants within the range of F. velutina, especially in Arizona, sometimes may appear close in

Nesom: Taxonomic status of Fraxinus c

morphology, at least superficially, to F. coriacea, but the two distinct geographic elements are clear

and the two taxa can be distinguished by the following contrasts.

1. Leaflet blades relatively thick, peltate scales somewhat sunken into abaxial q:?idermis, venation

distinctly raised on both surfaces; lateral petioiules 5— 10(— 13) mm Fraxinus coriacea

1. Leaflet blades relatively thinner, peltate scales superficial on abaxial epidermis, venation not
distinctly raised; lateral petioiules 0(-2) mm Fraxinus velutina

Fraxinus coriacea S. Wats., Amer. Naturalist 7: 302. 1873. Fraxinus velutina var. coriacea (S.
Wats.) Rehder, Proc. Amer. Acad. Arts 53: 206. 1917. Fraxinus pisiaciifolia var. coriacea
(S. Wats.) A. Gray, Syn. Fl. N. Amer. 2(1): 74. 1878. LECTOTYPE (Rehder 1917): USA.
Nevada. [Nye Co.:] Ash Meadows. 1871, Lieut. Wheeler s.n. (GH; isolectotype: NY digital
image!; probable isolectotype: GH!).

Fraxinus oregona var. glabra Lingelsh. ex Rehder, Proc. Amer. Acad. Arts 53: 207. 1917.
LECTOTYPE (designated here): USA. California. [Tulare Co.:] Along creeks, Greenhorn
Mountains, 3000^1000 [ft], Apr-Sep 1897, C.A. Purpus 5555 (US digital image!;
isolectotype: UC). Rehder also cited collections by Abrams (San Bernadino Co.) and Abrams
& McGregor (Los Angeles Co., San Bernadino Co.). He noted that an attempt by
Lingelsheim in 1907 to describe this species resulted in a nomen nudum. Lingelsheim (1920,
p. 43) still later treated F. oregona "Var. (3 glabra nov. var. Lingelsh." citing "(Parish n. 540!,
Wright!). — Scheint auf Californien beschrankt zu sein. — In Kultur noch selten."

Trees 5-10 m; twigs terete; bark light gray; winter buds brown. Leaves deciduous, pinnately
compound, 6-15(-20) cm, leaflets (3-)5(-7, rarely), yellow-green on both surfaces, glossy adaxially,
glabrous to sparsely to moderately hirteilous on both surfaces, not papillose, blades (2-)3- 10 cm x 2-
5.5 cm, broadly obovate to broadly elliptic-obovate or subrotund, apices obtuse or subtruncate to
long-acuminate, base obtuse to acute or acuminate, margins usually shallow!}' serrate on distal 1/2-
2/3 and often with apiculate teeth; petioles 15-35(-55) mm, bases slightly raised, leaf scars thin to
thick crescent-shaped, 3^1 mm wide; petioiules 5-10(-13) mm. Flowers unisexual (species
dioecious), appearing before the leaves, wind-pollinated; pistillate calyx ca. 1 mm, persisting at base
of samara; petals absent. Samaras 18-32 mm, bocH plump aiid ^ibc\iindtic 'Mn^s 2 giadualh
expanded from near the middle of the body, 4-6 mm wide at the widest point, often notched at the
apex. 2n = 46 (Wright 1957), 2n = 92 (Taylor 1945).

Flowering Apr-Jun. Sandy flats, gravelly washes, irrigation ditches, river banks, canyon
bottoms, cliff bases, desert shrub, chaparral, digger pine, digger pine-Douglas oak, ash-leaved maple;
(700-)800-1700(-2100) m; Ariz., Calif., Nev., Utah. Rqnorted from Baja California (Munz & Keck
1959; Wiggins 1980, "sw flank of the Sierra San Pedro Martir"). Welsh et al. (2003) noted that F.
velutina occurs in southeastern Iron Co. and western Kane Co. — I have not seen the specimens to
document this but they should be examined to confirm their distinction from F. c

Sin-eve and Wiggins (1964, p. 1087)) noted for Fraxinus velutina var, coriacea that "A
specimen that may belong here was collected in the foothills near the southwest flank of the Sierra

Wiggins (1980) also cited, "sw flanks of Sierra San Pedro

ACKNOWLEDGEMENTS

Specimens were studied from BRIT-SMU, GH, NY, SJC, TEX-LL, and UNM during visits
to those herbaria. I'm grateful to Robert George (BRIT) for help with technical problems and to
Nestor D. Perez-Moliere (NY) for the specimen images. This study w r as done in part under contract
for the Flora of North America Association, in conjunction with preparation of the FNANM treatment
of Fraxinus.

Nesom: Taxonomic status of Fraxinus c

LITERATURE CITED

Abrams, L. 1951. Illustrated Flora of the Pacific States, Vol. Ill, Geraniaceae to Scrophulariaceae.

Stanford Univ. Press, Stanford, California.
Holmgren, N.H. 1984. Oleaceae. Pp. 339-344 in A. Cronquist et al. (eds.). Intermountain Flora,

Vol. 4. The New York Botanical Garden, Bronx, New York.
Jepson, W.L. 1939. A flora of California. Vol. 3. Univ. of California, Associated Students Store,

Berkeley.
Lingelsheim, A 1920. Oleaceae-Oleoideae-Fraxineae. In A. Engier (ed.). Das Pflanzenreich IV

243: 1-61.
Little, E.L., Jr. 1952. Notes on Fraxinus (ash) in the United States. J. Wash. Acad. Sci. 42: 369-

380.
Little, E.L., Jr. 1971. Atlas of United States Trees, Volume 1: Conifers and Important Hardwoods.

USDAMiscell. Publ. 1146.
Miller, G.N. 1955. The genus Fraxinus, the ashes, in North America, north of Mexico. Cornell.

Expt. Sta. Memoir 335, Cornell Univ., Ithaca, New York.
Munz, P. A. and D.D. Keck. 1959. A California Flora. Univ. of California Press, Berkeley.
Munz, P. A and J.D. Laudermilk. 1949. A neglected character in western ashes (Fraxinus). Aliso 2:

49-62.
Owston, P.W. 1990. Fraxinus latifolia. In R.M. Burns and B.H. Honkala (tech. coords.). Silvics of

North America: 2. Hardwoods. USDA Forest Service Agric. Handbook 654. Washington,

DC.
Rehder, A. 1917. The genus Fraxinus m New Mexico and Arizona. Proc. Amer. Acad. Arts 53:

199-212.
Sargent, C.S. 1894, 1902. Fraxinus coriacea. Silva of North America. 1894. Vol. 6, p. 41; 1902.

Vol. 14, p. 33, plate 713.
Sargent, C.S. 1922. Manual of the Trees of North America (exclusive of Mexico) (ed. 2). Houghton

Mifflin Co., Boston and New York.
Shreve F. and I.L. Wiggins. 1964. Vegetation and Flora of the Sonoran Desert, Vol. 2. Stanford

Univ. Press, Stanford, California.
Taylor, H. 1945. Cyto-iaxonomy and phytogeny of the Oleaceae. Brittonia 5: 337-367.
Wallander, E. 2008. Systematics of Fraxinus (Oleaceae) and evolution of dioecy.

Plant Syst. Evol. 273 : 25-49.
Welsh, S.L., N.D. Atwood, S. Goodrich, and L.C. Higgins. 2003. A Utah Flora (ed. 3). M.L. Bean

Life Science Museum, Brigham Young Univ. Press, Provo, Utah.
Wiggins, I.L. 1980. Baja California. Stanford Univ. Press, Stanford, California.
Wilken, D.H. 1993. Oleaceae. Pp. 775-776 in J.C. Hickman (ed). The Jepson Manual: Higher

Plants of California. Univ. of California Press, Berkeley.
Wright, J.W. 1957. New chromosome counts in Acer and Frccdnus. Morris Arb. Bull. 8: 33-34.

Figure 1. Line drawing oiFraxinus coriaceaby Charles Faxon, from Sargent (1902).

Nesom: Taxonomic status of Fraxinus coriacea 6

Figure 2. Representative specimen of Fraxinus coriacea from Nye Co., Nevada (Roos 6082, NY).

Figure 3. Details of leaves (Nye Co.. Nevada. Roos 6082, NY) and
fruits (Clark Co., Nevada, Williams 80-32 J, NY)

status of Fraxinus coriacea

• Fraxinus latifolia
A Fraxinus coriacea
© Fraxinus velutina

Figure 4. County distributions (native range) of Fraxinus coriacea, F. latifolia, andF. velutina. The
range of F. velutina extends into Mexico. Welsh et al. (2003) noted that F. velutina (? = Fraxinus

a) also occurs in southeastern Iron Co. and western Kane Co., Utah — symbols in those

> are based on their report.

Nesom: Taxonomi

Figure 6. Detailed geographic distribution of
Fraxinus coriacea. Some localities have been
added from Munz and Laudermilk (1949); the
symbol for Baja California also is added from
literature; see notes in text.

Figure 5. Native range of Fraxinus latifolia,
from Owston (1990). The range is extended
southward in the present study (see Fig. 4 and
text).