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Full text of "Contributions to Pennsylvanian paleobotany: Notes on the Lepidocarpaceae"



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URBANA 



STATE OF ILLINOIS 

DWIGHT H. GREEN, Governor 

DEPARTMENT OF REGISTRATION AND EDUCATION 

FRANK G. THOMPSON, Director 

DIVISION OF THE 

STATE GEOLOGICAL SURVEY 

M. M. LEIGHTON, Chief 
URBANA 



CIRCULAR No. 73 
CONTRIBUTION TO PENNSYLVANIAN PALEOBOTANY 

NOTES ON THE LEPIDOCARPACEAE 

BY 

JAMES M. SCHOPF 



Reprinted from The American 
Midland Naturalist, Vol. 25, 
No. 3, pp. 548-563, May, 1941. 




PRINTED BY AUTHORITY OF THE STATE OF ILLINOIS 



URBANA, ILLINOIS 
1941 



Digitized by the Internet Archive 

in 2012 with funding from 

University of Illinois Urbana-Champaign 



http://archive.org/details/contributionstop73scho 



STATE OF ILLINOIS 

DWIGHT H. GREEN, Governor 

DEPARTMENT OF REGISTRATION AND EDUCATION 

FRANK G. THOMPSON, Director 

DIVISION OF THE 

STATE GEOLOGICAL SURVEY 

M. M. LEIGHTON, Chief 
URBANA 



CIRCULAR No. 73 



CONTRIBUTION TO PENNSYLVANIAN PALEOBOTANY 

NOTES ON THE LEPIDOCARPACEAE 

BY 

JAMES M. SCHOPF 



Reprinted from The American 
Midland Naturalist, Vol. 25, 
No. 3, pp. 548-563, May, 1941. 




PRINTED BY AUTHORITY OF THE STATE OF ILLINOIS 



URBANA, ILLINOIS 
1941 



Notes on the Lepidocarpaceae 1 

James M. Schopf 



Introduction 

Members of the Lepidocarpaceae are characteristic of the Eur-American 
floral province and are known to be present in both the Lower and Upper 
Carboniferous. Both in western Europe and in America recent records have 
added to our knowledge of this plant family, and it is now possible to present 
a discusison of the classification and evolution of the groups included in the 
lepidocarp alliance. It is the purpose of this paper to call attention to some of 
the bio-characters 2 which appear to be important in distinguishing lepidocarp 
genera but which have not been given equal consideration by different authors, 
thereby leading to some ambiguities and conflicting conclusions. It is hoped 
that this review will lead to greater consistency of treatment and to more rapid 
progress in understanding the geological and biological history of this group 
of plants. 

The writer wishes to acknowledge the help of Dr. J. Marvin Weller and 
thank him for critically reading the manuscript. 

The Lepidocarp Family 

The Lepidocarpaceae, like many other families of fossil plants, represent a 
group of indefinite taxonomic status. This family seems never to have been 
formally diagnosed, and hence its taxonomic validity has not been established 
beyond question — rather it has been a name denned through implications 
lent by the genera included in it. In the writer's opinion it comprises a group 
having undoubted natural affinity whose scope seems to be comparable to 
certain families of modern plants. The Lepidocarpaceae can be defined briefly 
as follows: 

Ligulate lycopsid plants, of arboreous or arborescent habit, producing male 
and female fructifications separately (probably never in the same cone, nor in 
juxtaposition on fertile branches equivalent to cones). Female fructifications 
specialized so that individual sporophylls or parts of them have assumed the 
essential characters of seeds in each of which only one megaspore normally 
matures. Sporangium indehiscent in the sense that the seed megaspore is not 
expelled; seed megaspore exceedingly large and lacking the thick impervious 
type of spore coat that characterizes the megaspores of free-sporing lycopsids. 

A rather sharp distinction should be made between the lepidocarp family 



1 Published by permission of the Chief, Illinois State Geological Survey. 

2 A bio-character is considered to be a definable unitary feature that has hereditary 
significance. 

548 



NOTES ON THE LEPIDOCARPACEAE 549 

(Lepidocarpaceae) and the other groups of Paleozoic lycopsids because the 
differences between lepidocarp fructifications and fructifications of all the ftee- 
spcring lycopsids appear to be valid criteria for at least family differentiation. 
The foregoing diagnosis of this family is, nevertheless, incomplete because 
definite knowledge of the vegetative characters is still lacking. It is hardly 
conceivable that the vegetative organs are wholly unrecognized in the fossil 
flora, but they are probably classified erroneously at present in some other 
family. 

The writer suspects that plants classified as Lepidophloios Sternberg 3 may 
be vegetative correlatives of genera belonging in the Lepidocarpaceae. Lepido- 
phloios scoticus Kidston is the only species of this genus whose fructification 
characters have been even partially ascertained. Its cones are borne on special- 
ized branches, an advanced mode of fructification not characteristic of Lepido- 
strobus or lepidodendrids in general. Nothing whatever is known, however, 
of the spores produced by these cones. L. scoticus is restricted to the Lower 
Carboniferous, the cones being known from oil shales of the Calciferous Sand- 
stone series in Scotland. At other localities and horizons the only evidence as 
to Lepidophloios fructifications still has to be deduced from association of 
disconnected fruiting structures. The lepidocarps, although they generally have 
passed unrecognized, appear to be among these associated types. In America 
Lepidophloios seems to be the only well represented group of lycopsids whose 
mode of fructification is so obscure. The lepidocarps, on the other hand, do 
not seem to have as plausible affinities with any other group based on vegeta- 
tive characters. 

The fact that the Lepidocarpacaceae and Lepidophloios coincide in their 
time range, both being limited to the Carboniferous and both being reasonably 
well represented throughout these beds, is perhaps as definite a point of 
evidence as can be cited now. Lepidophloios aff. L. laricinus (Sternb.) Stern- 
berg is a characteristic species found in roof shales over the Herrin (No. 6) 
coal which, in addition to the Mazon horizon, has also provided specimens 
assigned to Lepidocarpon mazonense Schopf. A form identified by Lesquereux 
as Lepidophyllum auriculatum (probably Lepidocarpon), was found at St. 
John (Perry County, Illinois, above No. 6 coal) closely associated with a 
species of Lepidophloios which Lesquereux (1870, p. 432, 439; 1880, p. 422, 
450) identified by the same specific name. He considered that the two species 
probably were correlated. Lepidophloios ranges through the English Lanarkian 
(which includes the "Lower Coal Measures") and is characteristic of the 
Lower Carboniferous where it is associated with Lepidocarpon (Walton 1935; 
Walton, Wier & Leitsch 1938). Other occurrences need not be cited here but 
the apparent association of these fossils may be significant. 

Correspondence that passed between the late Professor A. C. Noe and W. 
Hemingway of Derbyshire, England, concerning a shipment of sections sent 

3 Sternberg's original spelling of this name was "Lepidofloyos." There is a question 
whether the original spelling, or the now accepted "correction" of it should be used. I 
am indebted to Dr. F. C. MacKnight for calling this to my attention. 



550 THE AMERICAN MIDLAND NATURALIST 

Prof. Noe in 1925 contains a significant statement regarding the relations 
between Lepidophloios and Lepidocarpon. Mr. Hemingway wrote: 

Lepidocarpon "Lomaxi" represents quite a group of seed-like bodies and cannot yet 
be separated in sections. Lepidocarpon majus [n. comb.!] has been found attached to 
stems of Lepidophloios laricinus and Lepidocarpon lanceolatum [n. comb.] to Lepido- 
phloios acerosus. They are therefore the megasporocarps of Lepidophloios. 

Mr. Hemingway also stated: 

Lepidocarpon Lomaxi represents the "seed" of Lepidophloios — they have been found 
attached. The so-called species probably represents the seeds of several species of 
Lepidophloios. Lepidostrohus Oldhamius also represents the microspore cones of Lepi- 
dophloios and embraces several species. 

It may be that Mr. Hemingway had reference to the leaves at the tip of a 
vegetative branch of L. acerosus (L. & H.) Kidston (instead of "L. laricinus") 
that Kidston (1893, pp. 553, 559) illustrated and compared with Lepidophyllum 
majus Brongniart, and to the lanceolate leaves Macfarlane (1883) associated 
with Lepidophloios laricinus {^scoticus Kidston). If so, these associations 
perhaps have value only as analogies. Mr. Hemingway, however, has evidently 
also noted the lepidocarp characters commonly associated with the majus type 
sporophyll, and others which supported an identification with Lepidocarpon 
lomaxi. 

A few obvious lines of investigation suggest themselves for obtaining addi- 
tional evidence. To judge by the earlier papers of Kidston and others the cones 
of Lepidophloios scoticus are not rare. Even though they all may be immature 
when intact, evidence of the spores should be obtainable from them upon 
maceration. An attempt should be made to obtain compression specimens of 
Lepidocarpon from the Calciferous Sandstone series where they are to be 
expected because of their common occurrence as petrifactions. Mr. Heming- 
way's suggestion that Lepidocarpon lomaxi is separable into more definite 
species deserves consideration, and if the lomaxi group is reinvestigated, evidence 
bearing on the relationship of Lepidophloios also should be sought. It is partic- 
ularly important that the geological longevity of respective diagnostic bio- 
characters distinguishing the various intimately related species be investigated. 

If the suggested correlation of the genus Lepidophloios with several lepido- 
carpaceous genera be eventually substantiated it need occasion no great sur- 
prise. In the main it may be taken to indicate that in this Carboniferous group, 
as in modern plant groups, reproductive organs in general are more responsive 
to evolutionary change than are the vegetative ones. 

The oldest members of the lepidocarp family have been reported from the 
Calciferous Sandstone series of the Lower Carboniferous (Scott, 1900, 1901; 
also reported from Arran by Walton 1935, p. 318), and Cystosporites appears 
among the youngest members reported in Stephanian beds of Lower Silesia 
and the Saar district (recorded as Triletes giganteus; Zerndt, 1937, 1940) . The 
family is well represented in America both in beds of Pottsville and Allegheny 
age. Lepidocarpon also has been reported from Calhoun coal balls (Fisher and 
Noe, 1939) of probable upper Conemaugh age (cf. Schopf, 1941). Diversifi- 
cation seems more apparent within this family in America than in the old 



NOTES ON THE LEPIDOCARPACEAE 551 

world. This may be explained, in part at least, by the fact that the best fossil- 
iferous (coal ball) deposits in America are younger than those most studied 
in Europe, and these younger beds may contain representatives of the family 
at the apex of its geologic history. 

The Genus Lepidocarpon 

Lepidocarpon Scott, first recognized and denned about forty years ago, is 
the type genus of the Lepidocarpaceae. Scott's original diagnosis (Scott 1900, 
p. 309) is as follows: 

Lepidocarpon, gen. nov. — 

Strobilus, with the character of Lepidostrobus, but microsporangia and megasporangia 
each surrounded by an integument, growing up from the upper surface of the sporophyll. 
Megasporangium completely enclosed in the integument, except for a slit-like micropyle 
along the top. A single functional megaspore developed in each megasporangium. Sporo- 
phyll, together with the integumented megasporangium, detached entire from the strobilus, 
the whole forming a closed, seed-like, reproductive body. 

It is proposed to name the coal measures form Lepidocarpon Lomaxi and that from 
Burntisland L. IVildianum. Both were included by Williamson under his Cardiocarpon 
anomalum, which however, is quite different from the seed so named by Carruthers. 

Scott also noted on page 307 that "the outer layer of the sporangial wall 
has the columnar or palisade-like structure characteristic of Lepidostrobus; it is 
lined by a more delicate inner layer which may be several cells thick." 

In the diagnosis published with his more complete treatment of Lepidocar- 
pon (1901), Scott omitted mention of the microsporangiate structures because 
he was more doubtful of their relationship than he had been previously. The 
main points of his later diagnosis are as follows: 

(1) Strobilar habit — like Lepidostrobus; 

(2) Integuments present when mature; 

(3) Megasporangium entirely enclosed except for micropylar slit; 

(4) A single functional seed megaspore nearly fills the sporangial cavity; 

(5) Sporophyll became detached from the cone axis as a unit. 

To these an additional point may be added from p. 304 of Scott's detailed 
description. 

The structure of the sporangium is however the same, as in its naked condition 
[e.g., in Lepidostrobus] . The wall has a superficial columnar layer, with a more delicate 
lining tissue within it. The cells of the columnar layer are often shorter and broader 
than in the non-integumented sporangium [of Lepidoacrpon lomaxi] owing no doubt to 
superficial extension of the wall ; at other places, however, and especially at the apex 
where the narrow ridge of the sporangium fits into the micropylar opening, the structure 
is quite unchanged. 

In defining Lepidocarpon the writer considers it advisable to follow Scott's 
generic interpretation rather carefully. The diagnosis provided by Scott in 1900 
and slightly emended in 1901 may well be altered, however, so that it will 
reflect some of the additional observations made by various workers during the 
last forty years of sporadic study of this group of plants. It is now possible to 
refer compression and impression specimens to this genus and with the progres- 
sive elimination of non-biologic differences (resulting from differences of pres- 



552 THE AMERICAN MIDLAND NATURALIST 

ervation) the classification of these fossil plants becomes more truly phyletic. 
Lack of diagnostic information due to vagaries of preservation will probably 
always make it necessary to recognize non-biological distinctions to some extent 
in scientific classification. Lepidocarpon, however, appears to be an example 
where these differences can be relegated to less than generic importance. 

Lepidocarpon Scott (1900) 

(Revised diagnosis) 
A genus of ligulale lycopsid plants characterized by, 

(1) Strobilar habit of fructification; 

(2) Sporophylls attached to cone axis as in Lepidostrobus ; 

(3) Sporophylls shed entire by disintegration of the cone axis ; 

(4) Seeds provided with a distinct integumentary organ; 

(5) Integument, attached lateral to sporangium along pedicel, invests the sporangium 

closely and its trvo edges project ventrally above the seed body as a micropylar 
crest ; 

(6) Slit between the two membranes of the crest corresponding morphologically to a 

micro pyle ; 

(7) M egasporangium large, indehiscent (fertile spore not shed), attached for the 

greater part of its length to the ventral midline of the pedicel; 

(8) Outer wall of sporangium of prismatic or columnar cells, similar in structure to 

the sporangium wall of free-sporing lycopods; 

(9) Intrasporangial tissue more persistent than in most free-sporing lycopsids; 

(10) Seed megaspore relatively enormous (for lycopsids), spore coat with more or less 

fibrous texture and trilete apparatus at its proximal end (usually turned toward 
the anterior or distal end of the seed); 

(11) Maturation of only one seed megaspore per sporophyll, derived from a single 

tetrad; abortive megaspores also evident. 

English Species of Lepidocarpon 

The cone of the genotype species, Lepidocarpon lomaxi Scott, is medium 
sized (20-30 mm. diameter), of compact structure with sporophyll laminae 
long and strongly reflexed upwards. Toward the tip of each lamina the blade 
seems to have been membranous and impersistent but near the seed it was 
rather fleshy and is commonly well preserved. Mature seeds are fully integu- 
mented but the integument is frequently incomplete on immature specimens, 
and in this condition it is represented by fleshy cushions along both sides of 
the pedicel. The integument is presumed to have been formed last, late in 
ontogeny. A simple layer of columnar or prismatic cells, very similar to the 
prismatic layer of Lepidostrobus, covers the sporangium. Radial length of fruit 
is 8-14 mm., - — tangential height through seed body 5-11 mm., — width at 
distal end of seed body 5-12 mm. This species occurs in the English "Lower 
Coal Measures." It has been reported in most coal seams of this age that have 
provided coal balls, and thus it must be considered a rather widespread and 
characteristic element of the upper Lanarkian flora. 

Scott also described a second much older species, L. wildianum, from the 
Calciferous Sandstone at Pettycur that is somewhat smaller than L. lomaxi, 
but otherwise not readily distinguishable. The seed megaspore shows an "irreg- 
ular reticulation" (Scott, 1901, p. 315) which in all likelihood is similar to the 
fibrous network composing the Cystosporites membrane. L. wildianum is doubt- 
less a distinct species, and future studies will probably make known biological 



NOTES ON THE LEPIDOCARPACEAE 553 

characters by which it can be recognized, but at present its true distinguishing 
characters are not known. More thorough examination of Lanarkian forms will 
probably also result in additional species being recognized, as suggested by Scott 
and others who have examined many "Lower Coal Measures" specimens. 

For convenience L. lomaxi, L. wildianum, and closely related but as yet 
undistinguished forms of Lower Carboniferous and Lanarkian age will be 
referred to as the lomaxi group. Because they possess certain characteristics 
reminiscent of those of free-sporing lycopsids and, in addition, because of their 
antecedent stratigraphic position relative to the American species, they are 
regarded as examples of the more primitive lepidocarp stock. 

In 1914 Kidston described Lepidocarpon westphalicum from the Yorkian 
age ironstone deposits near Dudley. The type consists of an axis with scars 
of sporophylls previously shed and a central portion on which parts of about 
twenty attached sporophylls are visible. The cone is of compact construction 
and is preserved without crushing, but only surface features were observed and 
these are not all that might be desired The laminae may be of moderate length 
and appressed to the cone, judging from Kidston's Figs. 1, 3, 4, and 5, where 
they seem to appear in lengthwise fracture on both sides of the specimen. 
Kidston states that the "whole of the bracts have disappeared" and so the 
laminae, apparently seen, may be illusory. The laminae, however, may have 
been membranaceous distally, similar to those of L. lomaxi described by Scott. 
The particular feature that decided Kidston on the generic identification of 
this species was the sporangial integument, but he did not note a micropylar 
slit. So far as known the integument appears generally similar to that of L. 
lomaxi. Most of the sporangia have their disal ends exposed, and on many of 
these a small terminal irregularity appears which should be opposite the trilete 
apparatus of the seed megaspores inside them. 4 No remnants of the se.ee! 
megaspores have been reported in Lepidocarpon westphalicum although they 
may be present. There are no very definite biological characters distinguishing 
L. westphalicum from members of the lomaxi group except for differences in 
size. The cone is about 15 mm. in diameter in contrast to 20-30 mm. for L. 
lomaxi; tn*» sporangia are smaller and have a height-breadth ratio of l 1 ^ to 1 
whereas in L. lomaxi the ratio is slightly less than 2 to 1. 

Records of American Lepidocarpaceae 

Lepidocarpon was first reported in America by Noe (1931) in a list com- 
piled from investigations by certain of his students. A discussion of this 
material was included in Miss Krick's (1932) report on seed-like fructifica- 
tions from the Harrisburg (No.5) coal in Illinois. Later Fredda Reed (1936) 
described other isolated Lepidocarp sporophylls from the same source. The 
presumptive evidence that these specimens belong to Lepidocarpon is good, 
but it can not be considered entirely conclusive because the manner of pedicel 

4 These may be the "smooth pits at the basal end" which Darrah (1941, p. 87) 
refers to as sporangial attachment marks but this interpretation is not indicated by Kid- 
ston's discussion. 



554 THE AMERICAN MIDLAND NATURALIST 

attachment was not demonstrated in either case. The importance of such attach- 
ment was not then realized, and it is probable that the specimens studied by 
both of these authors were attached to a cone axis in the true Lepidocarpon 
fashion. Miss Reed has recently demonstrated such attachment for other Harris- 
burg specimens by means of an adequate series of tangential slices described 
at the 1939 meeting of the Paleobotanical Section. The importance of pedicel 
attachment in the lepidocarps is emphasized below in connection with the 
discussion of Illinio carport. 

Both Noe and Krick identified their lepidocarp material as Lepidocarpon 
lomaxi Scott. This specific identification is doubtful, however, because the 
similarities mentioned by Krick concern chiefly the size of the seed body. 
Without supporting evidence this cannot be regarded as positive proof of 
specific identity. The histological details particularly must also be carefully 
considered. The Harrisburg material appears to be significantly younger than 
the "Lower Coal Measures" specimens studied by Scott. 

The sporophylls described by Fredda Reed (1936) were not specifically 
identified. They appear to correspond with immature and abortive megasporan- 
gia such as Scott reported for L. lomaxi. However, the sporangium wall had a 
sclerotic rather than a prismatic external layer of cells. This may be a feature 
of considerable significance in lepidocarp evolution, inasmuch as it indicates 
the loss of a primitive character well represented in the lomaxi group. 

The writer described two new species belonging to the Lepidoearpaceae in 
1938 (Schopf, 1938a). One (L. mazonense) is a form common in the Mazon 
concretions above the Colchester (No. 2) coal in Grundy and Will counties 
wnich resembles in many respects the generalized type traditionally known as 
Lepidophyllum majus. Its reference to Lepidocarpon was definitely established 
although it is not certain that this species is distinct from earlier described but 
less adequately understood forms. Lepidophyllum majus itself is confused taxo- 
nomically because the type is a poor specimen with the seed body missing; it 
was originally designated Filiates (Glossopteris) dubius by Brongniart (1822), 
and its name was later changed in the Prodrome (1828, p. 87). It would prob- 
ably be impossible to prove that the Mazon form is cospecific with the type, 
even if such were actually the case. Certainly some of the specimens referred 
to L. majus are not cospecific with Lepidocarpon mazonense, although there is 
no reason for believing them to be generically distinct. Probably Brongniart's 
species will pass into disuse because of the inconclusive nature of its type and 
the consequent doubt as to its accurate specific definition. 

A brief description of a new type of lepidocarp seed was presented in the 
same publication (Schopf, 1938a). This differs significantly from the genus 
Lepidocarpon and a new generic name, llliniocarpon, was given it. In trans- 
verse sections through certain parts of the seed body it closely resembles 
Lepidocarpon, but a qualitative and diagnostic difference appears in the manner 
of sporophyll attachment to the fertile branch. This distinction is commonly 
shown in longitudinal sections, and single transverse sections of either Lepido- 
carpon or llliniocarpon cannot be counted on to provide conclusive evidence of 



NOTES ON THE LEPIDOCARPACEAE 555 

the distinction between the two genera. The individual sporophylls (not cones) 
of Illiniocarpon are properly described as pedunculate, and by modification of 
the pedicel and other changes these plants have lost the strobilar habit of 
fructification to a significant degree. The integumentary organ (which, as Scoct 
emphasized, is not merely the upturned margin of sporophyll lamina) is more 
specialized, and the actual lamina is extended, broad, and doubtless served as 
a wing for dispersal of the fruit after it had been shed as a unit from the 
fertile branch. The laminae of some Lepidocarpon species also probably served 
this same function [e.g., L. mazonense, (?) L. linearifolium (Bassler)] and 
thir- may perhaps be regarded as a miner example of evolutionary parallelism 
in the two groups. 

Numerous large fibrous sack-like bodies (seed megaspores) with trilete 
appartus at one end similar to those Zerndt (1930) described as Triletes 
giganteus have been obtained by the writer from maceration residues of coal. 
These seed megaspores are closely related to Lepidocarpon mazonense but 
because essential diagnostic characters can not be established and because these 
isolated seed megaspores appeared to be moderately generalized, it has seemed 
unwarranted to identify them with either of the two genera that had been 
previously recognized in the Lepidocarpaceae. Their characters, however, fully 
supported their reference to this family, and the genus Cystosporites was 
proposed for their reception (S'chopf, 1938b). This genus maybe entirely or 
only in part equivalent to the Lepidocarpaceae but it clearly exceeds the scope 
of other genera more adequately diagnosed on the basis of their sporophyll 
structure. Biologically it appears to overlap both of the established genera, and 
the isolated spores are thus classifiable with less precision thin is possible 
where complete fruits are available, but for scientific reporting a name is none 
the less essential for them. It is incorrect to assume that Cystoporites is 
only the seed megaspore of Lepidocarpon (Darrah 1941, p. 89), because its 
relationship is definitely broader. The significant contribution aJorded by the 
recognition of Cystosporites is that it shows best how geologically long lived 
and widespread the Lepidocarpaceae were in Carboniferous times (cf. Schopf 
1938b; Zerndt, 1937, p. 68; 1940, p. 142). Not only is Cystoporites a practi- 
cal generic designation of use in classification of these isolated seed megaspores, 
but it also indicates a group of natural affinity and certain bioogical signifi- 
cance. The delimitation of its natural affinity is in fact far more precise than a 
great many other generic groups commonly used in the ckssificition of fossil 
plants. It should be recognized that the introduction of such a genus is not a 
"purely artificial method of classification" and that plants which have been 
classified as Cystosporites do not already possess any other properly assignable 
generic names. 

In 1938 the writer discovered that the holotype of Carpolithes corticosus 
Lesquereux is clearly cospecific with a form previously discovered in the 
Mazon shale which he had interpreted as a variant of L. nazoiense. Further 
study showed conclusively that Lesquereux' species was quite dstinct from L. 
mazonense. Later, when Janssen's treatise on certain of the Lsquereux types 
war in preparation, the writer was invited to contribute a revisim of this form, 



556 THE AMERICAN MIDLAND NATURALIST 

and the species was transferred to the genus Lepidocarpon (Schopf, in Janssen, 
1940). Lepidocarpon corticosum (Lesq.) Schopf is most closely related to L. 
novaculeatum and L. robustum both of which were transferred from Bassler's 
genus Cantheliophorus^ which is discussed on a later page. An abortive mega- 
spore from the original tetrad is present in its normal position near the anterior 
of the seed body in the holotype of L. corticosum in addition to the large 
fertile one. L. mazonense and L. corticosum furnish substantial proof that 
histological features are not essential for recognition of this genus, and in this 
respect Kidston's generic identification of L. westphalicum is confirmed. 

Darrah has recently described a new species under the name of Lepido- 
carpon glabrum (1941). Although cellular detail is preserved in his specimen 
few characters were available for distinguishing this species and consequently 
its generic classification deserves more critical examination. This plant has 
seeds which consist (so far as the types at least are concerned) of a sporangium 
with well developed internal tissue surrounding the seed megaspore. No infor- 
mation as to the pedicel, lamina, or axial attachment of the complete sporophyll 
is provided nor is there any evidence of the integuments that characterize 
mature seeds of all other members of the genus. 6 

llliniocarpon was distinguished from Lepidocarpon (1) because the sporo- 
phyll was pedunculate in one and normally situated on a strobilar axis in the 
other; (2) because in llliniocarpon the integuments are separately vascularized 
posterior from the peduncle and are developed differently, being far more 
evaginate; (3} the sporophyll lamina in llliniocarpon is straight and not 
reflexed as in Lepidocarpon. (4) Apparently correlated with this last character 
is a further specialization of the sporangium wall near the ligular region at the 
anterior end of the seed which has not yet been found in Lepidocarpon. 

Lepidocarpon glabrum is inadequately known regarding (1) strobilar (com- 
pact, lax) or non-strobilar habit, (2) presence, absence, or nature of the true 
iepidocarp integument, and (3) character of the lamina. It cannot be positive- 
ly identified -vith Lepidocarpon because these important diagnostic characters 

5 The writer is not quite certain, that Bassler's L. robuslum and L. novaculeatum 
are specifically distinct from each other or from L. corticosum. The relationship in any 
case is evidently very close. However there seems to be ample basis for specific dis- 
crimination betveen the other forms Bassler described. Nevertheless, the arrangement of 
plates and destriptne data is such that careful study of Bassler's paper is required in 
order to clearlr establish the specific differences. 

6 Darrah las described the external layer of the sporangial wall as the "integu- 
ment." From a purely descriptive standpoint the term may be so used, but it is inadvis- 
able because ill other Lepidocarps have a distinct organ, called the integument by 
most writers, tlat is entirely separate from the megasporangium. Specimens of Lepido- 
carpon glabrun, do not now possess any integument of this sort. Whether the sporangia 
were originally integumented when the sporophyll was complete is unknown, although 
from Darrah's accoant it seems unlikely that they were. 

Darrah alst infers (op. cit. p. 95) that the sporangial wall of Lepidocarpon 
includes sclerotc "protective tissues." Scott's description of specimens of the lomaxi 
group do not stpport this conclusion and in only one form (aside from L. glabrum) 
has sporangial w/1 sclerenchyma appeared (Reed, 1936). 



NOTES ON THE LEPIDOCARPACEAE 557 

have not been observed. Characters other than those of the seed megaspores 
are shown, however, so that the species is classifiable with more precision than 
is possible when only isolated seed megaspores are present. Positive differences 
are exhibited which may have significance of more than specific value. The 
seeds of L. glabrum are mature, and the individual sporangia (evidently not 
entire sporophylls) have been shed. There is no previously described species of 
recognized lepidocarps in which shedding of mature sporangia apart from their 
integument was possible. The number of isolated sporangia which Darrah 
records indicates decisively that shedding of the individual sporangia was a 
normal occurrence in this species. The only mark reported on the mature 
sporangial seed (which in this species is equivalent only to a ripened ovule — 
without the additional sporophyll parts possessed by seeds of other lepido- 
carps) is at the point of its attachment to a pedicel or pedicel-equivalent. 
Mature megasporangia (seeds) of Lepidocarpon or Illiniocarpon were not so 
separated from their sclerous integuments. Abortive and immature sporophylls 
of L. lomaxi commonly lack the integument, but junctional seeds are equipped 
with them. Typical Lepidocarpon sporangia are not sclerotic but have walls 
whose prismatic layer is strikingly similar to that of Lepidostrobus. Their 
preservation appears primarily to result from the efficient protection of the 
integumentary organ. 

Darrah's illustrations and description of the wall of L. glabrum sporan- 
gia (seeds) thus suggest that they differ considerably from sporangia of the 
lomaxi group. The unintegumented sporophylls described by Fredda Reed also 
are noteworthy in their lack of a prismatic sporangial coat. Similar sporangia 
of the lomaxi group described by Scott possess a somewhat thicker sporangial 
wall tissue than the integumented forms, but the prismatic layer apparently is 
developed typically in all. Illiniocarpon shows a different type of modification 
in the sporangial wall. In the lower anterior region the wall is thick, and 
although the prismatic layer is easily recognized it is considerably modified 
and possesses larger cells with undulant walls (cf . Fig. 9; Schopf, 1938a) . The 
anterior prongs show rather typical prismatic (columnar) structure but the 
posterior part of the sporangium wall is more delicate and can hardly be consid- 
ered prismatic. In fact it resembles the epidermal layer of a well protected 
ovule. This is what would be expected if the lepidocarp sporangium were modi- 
fied in accordance with the degree of exposure and protection afforded by the 
integument. The adaxial ("posterior") part of the seed body in Illiniocarpon 
is well enclosed and probably was somewhat better protected than in Lepido- 
carpon, but the anterior part of the seed (facing the lamina) may have been 
more exposed because the sporophyll lamina was not reflexed upwards around 
it. Evidently the character of the sporangium wall deserves more thorough 
study in the lepidocarps because it probably reflects the type of seminal modi- 
fication. 

Intrasporangial tissue within the dermal layer in Lepidocarpon glabrum 
also appears to be a significant character. In the unintegumented sporangia of 
the lomaxi group the sporangial tissue is consistently thicker than in the integ- 
umented seeds, and this was explained on physiological- ecological grounds. In 



558 THE AMERICAN MIDLAND NATURALIST 

L. glabrum, however, this tissue is so much more developed that the character 
has probably become hereditary. Concordantly the seed megaspore of L. 
glabrum also occupies proportionally less space in the sporangium than in 
those of other lepidocarps. This appears to be true, at least in so far as the 
sections shown on Darrah's Plate II are typical of the species. In the lomaxi 
group and in Illiniocarpon there is no comparable development of the "nutri- 
tive" tissue. 

Darrah's species therefore probably lacks diagnostic features which assured- 
ly would place it in the genus Lepidocarpon and in addition shows other modi- 
fications which indicate considerable divergence from that group. Because of 
the lack of a prismatic palisade layer, Fredda Reed's specimens may occupy an 
intermediate position between Lepidocarpon Scott and Darrah's divergent 
type, L. glabrum. It is important that the divergent characters of the latter 
be recognized, and the writer regards them, in conjunction with the lack of 
information in other particulars, as conclusively indicating a need for L. 
glabrum, at least, being classified under a distinct generic name. However, 
there is no basis for doubting that its relationship is definitely with the Lepido- 
carpaceae. 

Darrah's comparison of Lepidocarpon glabrum with Lepidocystis is highly 
significant, and it may be that this ambiguous and poorly defined group will 
be clad with useful biological meaning after all. The Lepidocarpon described 
by Reed from Harrisburg coal balls, which also lacks a prismatic sporangial 
wall, is not integumented and may not be abnormal as Reed supposed. It also 
might be classified with this divergent lepidocarp group having "lepidocystoid" 
characters. However, there appears to be considerable disharmony among speci- 
mens which have been labeled "Lepidocystis" in the past. Few of them have 
been shown to possess spores in place, but those specimens in which spores have 
been recognized are clearly referable to the free-sporing lycopods, probably to 
the Lepidodendraceae. It is altogether possible (in fact, probable, in view of 
L. glabrum) that many specimens which do not appear to have spores, actually 
enclose unrecognized seed megaspores of the cystosporean type. These speci- 
mens would necessarily belong in the Lepidocarpaceae. The availability of the 
name Lepidocystis for lepidocarp species with this latter character evidently 
must be determined by restudy of the genotype which is Lepidocystis pectinatus 
Lesquereux. 7 

The conclusion that there are at least two divergent branches of the primi- 
tive integumented lepidocarp stock in the American Pennsylvanian is plausible. 
One branch shows greater specialization of the integuments and other struc- 
tures and is represented by Illiniocarpon. The other branch is represented by 
L. glabrum in which the seeds have been subject to a different kind of speciali- 
zation involving, probably, loss of the integument. Presumably the less special- 
ized true Lepidocarpon type coexisted with both of the more specialized line- 
ages, but the ancestry of the latter groups may be sought among the more 
primitive lepidocarps that geologically antedate them. 

7 The holotype of this species is listed in Lesquereux' "Coal Flora" as No. 423 
of the Lacoe collection, now in the U. S. National Museum at Washington, D.C. 



NOTES ON THE LEPIDOCARPACEAE 559 

Cantheliophorus and Lepidocarpon 

A substantial addition to the Lepidocarpaceae was made by Harvey BassJer 
(1919) in his description of twelve species under the generic name of Canthe- 
liophorus, although he misinterpreted the structure of his material. 8 Bassler 
recognized that his species were highly specialized and his statement (1919, 
p. 97) that "members of a group with structure as intricate and diverse as this 
will have high stratigraphic value if treated with great systematic refinement" 
seems more than ever warranted. 

Lepidocarp sporophylls in shale are preserved differently, depending upon 
whether the plane of rest is determined by a broad lamina or by the form of 
the seed body itself. The seed body generally is higher than broad, and if the 
lamina forms too narrow an appendage, the height of the seed body is most 
likely to parallel the bedding. All of Basser's species seem to have been pre- 
served in this position and those he illustrates are compressed parallel to the 
organic longitudinal plane. Thus they appear much different from most speci- 
mens of Lepidostrobophyllum in which the laminal breadth more consistently 
parallels the bedding planes. Although characters of size and proportion of 
sporophyll laminae are generally considered to be of specific importance, they 
probably lack generic significance. 

The features Bassler considered to be unique in Cantheliophorus were, (1) 
two sac-like sporangia per sporophyll, borne on short sporangiophoric stalks; 
(2) a plate of sterile sporophyll tissue ascending from the ventral midline of 
the pedicel and to which the sporangiophores were attached laterally and dis- 
taily. The structures ilustrated, however, do not support this morphologic 
interpretation of them. They are instead more satisfactorily explained by com- 
parison with Lepidocarpon, and according to this interpretation they comply 
entirely with the essential diagnostic characters of that genus. Bassler has not 
presented evidence proving the existence of two sac-like bodies on any single 
sporophyll - — he has not shown the "median" plate to be other than the 
compressed form of the Lepidocarpon integument. 

The "sporangia" of Cantheliophorus agree precisely with seed megaspores 
of the lepidocarps, and they must be interpreted in this light. It is understand- 
able how Bassler and others failed to note this resemblance because no lepido- 
carp megaspores had been isolated previously and they are remarkable objects 
e.uite different from the common free-sporing forms in general outline and size. 
Nevertheless the single fertile lepidocarp seed megaspore is clearly recognizable 
from Bassler's figures for most of the Cantheliophorus species. They agree in 
habit with those the writer has illustrated from Lepidocarpon corticosum 
(Schopf 1938a, 1938b, 1940) and also with seed megaspores obtained from L. 
mazpnense. The agreement with seed megaspores Bocheriski (1936) obtained 



8 Bassler's descriptions are given in terms of his hypothetical interpretation of the 
sporophylls, but there is no reason for preserving this terminology because his specimens 
are easily described by other terms that were previously and still are in good technical 
usage. 



560 THE AMERICAN MIDLAND NATURALIST 

from lepidocarp cones in the Lower Silesian coal field is just as striking. 9 

This striking agreement is by no means limited to the seed megaspores but 
continues in remarkable detail to all other portions of the lepidocarp sporo- 
phylls and is perhaps best illustrated by comparison with a larger species of 
Lepido car port (as yet undescribed) represented by numerous examples in the 
Illinois Survey collections from near Wyoming Hill (Muscatine County) 
Iowa. The latter specimens are compressed in a dark fissile shale and thus 
entirely agree with Bassler's in mode of preservation, even showing similar 
lengthwise folding of the sporophyll laminae. Where the shale is intact these 
sporophylls contain well preserved lepidocarp seed megaspores. On mild macer- 
ative treatment the fibrous megaspores of cystosporean type are easily isolated; 
they show the characteristic trilete commissure at the apex and are associated 
with abortive tetrad members. The "plate" Bassler described is represented in 
these specimens (just as it is shown in his illustrations of Cantheliophorus) by 
a very definite micropylar crest which is similar to that unmistakably shown in 
Ltpidocarpon mazonense. The coaly and external integumentary impression 
surfaces of Wyoming Hill shale specimens agree absolutely with Bassler's 
figures and characterization (op. at., p. 79) as "usually granulose to the 
unaided eye and minutely rugulose-bullate under the lens." Observation under 
the Greenough microscope shows the surface rugosity is due to the type of 
sclerotic cells present on integumentary surfaces. Lepidocarpon corticosum 
(Lesq.) although preserved a little differently also is similar to Bassler's 
material in many respects. 

Such precise agreement and the absence of any conflict in generic characters 
indicate that species of Cantheliophorus Bassler must be referred to the older 
genus Lepidocarpon Scott, and this has been proposed in an earlier publication 
by the writer (Schopf, in Janssen, 1940). The geologic time range of Canthe- 
liophorus species is entirely that of Lepidocarpon, and there is no reason for 
concluding that Cantheliophorus is in any biological way distinct or distinguish- 
able from Scott's genus. 

Darrah (1941, p. 89) recently has stated, that "a number of sporophylls 
of the Cantheliophorus type . . . bear many megaspores of the familiar 'Tri- 
letes' type" and on this account he does not accept the synonymic reference of 
Cantheliophorus to Lepidocarpon. It is difficult to understand how any sporo- 
phyll bearing numerous Triletes-type megaspores can justifiably be assigned to 
Cantheliophorus or to Lepidocarpon. Bassler found none in the examination 
of a large suite of specimens, and in failing to definitely recognize spores of 
any sort, concluded (op. cit., p. 81) that the plants probably were homospor- 
ous. It would seem that no matter what apparent similarities there may be 
between the superficial form of the sporophylls, no free-sporing plant can be 
assigned to Lepidocarpon (or to Cantheliophorus which is in complete synony- 

9 Bochenski assigned these specimens to Lepidostrobus and compared the spores with 
Trileles giganteus Zerndt and Sporites varius Wicher, but his specimens also must be 
identified with Lepidocarpon. There is a great difference between the spores he isolated 
from these specimens and the free-sporing Trileles and Sporites genotypes, and lepido- 
carp megaspores now may best be compared with Cystosporites, a genus which, in part, 
was proposed for reception of Zerndt's and Wicher's species. 



NOTES ON THE LEPIDOCARPACEAE 561 

my with it) . The presence of free-sporing megaspores is a character which not 
only excludes a plant from these genera but also places it beyond the family 
limits of the Lepidocarpaceae. 

Summary 

Family characteristics of the Lepidocarpaceae are given. It is suggested 
that Lepidophloios is a possible lepidocarp representative showing the vegeta- 
tive features of these plants. The diagnostic characteristics of Lepidocarpon are 
reviewed, and the generic diagnosis is rephrased. The essential distinctions Scott 
recognized in establishing the genus are entirely valid and should be adhered 
to rather closely. 

The genera and species discussed include Lepidocarpon lomaxi, the geno- 
type of the type genus for the family, L. wildianum, and L. westphalicum, all 
known from English sources. Records of Lepidocarpon in America are reviewed 
with respect to the characters used in their identification. Points which distin- 
guish Illiniocarpon from Lepidocarpon are enumerated and the relationship of 
these genera with the less precisely denned genus Cystosporites is restated. 
Attention is called to divergent characteristics of Lepidocarpon glabrum from 
Iowa, and possibly also represented to a lesser degree in another lepidocarp 
from Harrisburg coal balls, which would seem to set them apart from the 
genus Lepidocarpon. Reasons are given for referring the American forms 
named Cantheliophorus to Lepidocarpon. 

American lepidocarps in particular are worthy of intensive study because 
the diversified forms present a particularly interesting problem of plant evolu- 
tion. In the following tabulation of the Lepidocarpaceae each species is listed 
according to its approximate age. The larger number of forms occurring in 
post-Pottsville beds supports the conclusion that diversification was more rapid 
during that time. 

Post-Pottsville (Post-Westphalian B) 

Lepidocarpon mazonense Schopf Illiniocarpon cadyi Schopf 

L. corticosum (Lesq.) Cystosporites breretonensis Schopf 

L. novaculeaium (Bassler) C. giganteus (Zerndt) 

L. robustum (Bassler) Lepidocarpon lomaxi (?) 
L. subulatum (Bassler) (Noe, Krick, Fisher & Noe) 

L. linearifolium (Lesq.) L. sp. Reed 

L. sicatum (Bassler) — L. (?) glabrum Darrah 
(also in upper Pottsville) 

Pottsville 
(Mid-Lanarkian to Staffordian ; Mid-Namurian to Westphalian C) 

Lepidocarpon Tvestphalicum Kidston Lepidocarpon grande (Bassler) 

L. lomaxi Scott L. ensiferum (Bassler) 

L. Toaldenburgense (Potonie) L. pugiatum (Bassler) 

Cystosporites giganteus (Zerndt) L. ioroense Hoskins & Cross 

(of Pottsville age*) 



* For description see Amer. Midi. Nat. 25(3) :543, 1941. (Horizon information 
fide Cross June 9, 1941.) 



562 THE AMERICAN MIDLAND NATURALIST 

Lower Carboniferous (Mississippian, in part) 

Lepidocarpon mirabile (Nathorst) Lepidocarpon riparium (Nathorst) 

Lepidocarpon Tvildianum Scott — (Calciferous Sandstone). 



REFERENCES 

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Bot. Soc. Edinburgh 14:181-190. 

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ScHOPF, J. M. 1938a — Two new lycopod seeds from Illinois Pennsylvanian. Trans. 
Illinois Acad. Sci. 30(2) : 139- 146. 

1938b — Spores from the Herrin (No. 6) coal bed in Illinois. Illinois Geol. 

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1940 — Lepidocarpon, in Janssen, R. E., Some fossil plant types of Illinois. 

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NOTES ON THE LEPIDOCARPACEAE 563 

1901 — On the structure and aff. etc. — IV. The seed-like fructification of Lepido- 

carpon, a genus of lycopodiaceous cones from the Carboniferous formation. Phil. 
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Walton, John. 1935 — Scottish Lower Carboniferous plants: the fossil hollow trees 
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Zerndt, Jan. 1930 — Triletes giganteus, n. sp., eine riesige Megaspore aus dem Karbon. 
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1937 — Les megaspores du bassin houiller Polonais, Deuxieme Partie. Acad. 

Polonaise Sci. et Lett., Comite des publications Silesiennes — Trav. Geol. No. 
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1940— Megasporen des Saarkarbons. Palaeontographica 84, Abt. B: 133-150, 

Stuttgart. 



Coal Division, 

Illinois State Geological Survey, 

Urbana, Illinois. 



"WASCHER'S" 

EBSARY BINDERS 

507 S. Goodwin 

Urbana, I1L