Diaphorodendron, gen. nov., a Segregate from Lepidodendron (Peiiiisylvaiiian Age) STOR

William A. DiMichele

Systematic Botany, Vol. 10, No. 4 (Oct. - Dec, 1985), 453-458.

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DiAphorodendron, gen. nov., a Segregate from Lepidodendron (Pennsylvanian Age)

WILLIAM A. DIMICHELE Department of Botany, UaLversity of Washington, Seattle, Washington 98195

ABSTRACT. Diaphorodendron is described as a new genus on the basis of anatomically preserved specimens previously included in Lepidodendroti. Species include D. vasculare (type species), D. sderolii^tiW., D. dicentricum, and D. phillLpsii. Circumscription of this new genus leaves Lepidodendron as a monophyletic, morphologically cohesive taxon. Traditionally Lepidodendron has been recog- nized by its higher-than-wide leaf cushions, a character that appears to be the ancestral (pleslo- morphic) state in the Lepldodendrales. The consequence of relying on this single trait has been inclusion of forms distinct in most aspects of basic morphology within Lepidodendron, masking rather extensive diversification in the Lepidodendrales. While sharing basic leaf-cushion shape, Diaphorodendron and Lepidodendron differ in. many anatomical features and details of leaf-cushion, morphology (especially relative "thickness" of leaf cushions and presence or absence of infrafoliar parichnos). By correlating anatomy and leaf-cushion morphology, characteristics can be recognized by which Diaphorodendron and Lepidodendron can be distinguished in compression preservation.

The purpose of this report is to establish a was associated with leaf cushions having height new generic name for a distinctive, structural- to width ratios greater than one {the principal ly-preserved group of Pennsylvanian-age lep- character by which Lepidodendron was recog- idodendrid lycopods previously included in the nized). They concluded that anatomy varied genus Lepidodendron Sternberg. The species that greatly within a genus and therefore was not form the nucleus of this segregate genus are useful in distinguishing genera of lepidoden- Lepidodendron vasculare Binney, L. sderoticum drids. This view has prevailed in the literature Pannell, L. phillipsii DiMichele, and L. dicentri- until recently even though it would appear cum Felix {=L. schizostelicum Arnold) {see more reasonable to conclude that the character DiMichele 1979b, 1981, 1983a). of having higher-than-wide leaf cushions is in- Historical factors have confused and compli- appropriate for delimiting Lepidodendron. cated the taxonomy of lepidodendrids. This is The extensive anatomical data base can be most apparent in the application of taxonomic used to resolve questions of lycopod taxonomy concepts based on compression-impression if anatomically preserved leaf-cushion mor- specimens to anatomically-preserved speci- phologies are characterized in such a way that mens. Compression specimens display only ex- they can he compared to the compression rec- ternal morphology; many such characters po- ord. This, in turn, would allow correlation of tentially have a high degree of covariation and compression taxa with more broadly-circum- probable correlation {leaf cushion traits such as scribed anatomical taxa, and improve our un- height, width, etc.). Anatomically-pre served derstanding of the taxonomic significance of specimens offer a much larger suite of charac- variability in leaf-cushion form. For example, ters for comparison, and include most of those the type species of Lepidodendron, L. aculeatum that can be observed in compressions. Generic Sternberg {Thomas 1970), is based on compres- concepts in lycopods, in almost all cases, were sion specimens. While several distinctive ana- first established on the basis of compression tomically-based taxa have leaf cushions that are specimens. Thus, the application of names be- higher than wide, only one, Lepidodendron hickii tween preservational-types has been largely Watson, has leaf cushions with the character- unidirectional. Names used for compression- istics found only in L. aculeatum and similar impression specimens have been used to en- compression forms: radially raised or protrud- compass anatomically preserved forms. One of ing leaf cushions that bear infrafoliar parich- the best examples of this is provided by Lepi- nos, and that change shape from slightly elon- dodendron. Scott (1906) and Seward (1906) not- gate on small branches to relatively more ed that more than one distinct kind of anatomy elongate on larger stems (Watson 1907; Di- 453 454 SYSTEMATIC BOTANY [Volume 10

Michele 1983a). Height to width ratio alone will In a series of earlier articles I have attempted not permit correlation of the type species of to re-circumscribe these forms and illustrate that Lepidodendron with one of the several distinct no intermediates have yet been found (Di- kinds of stem anatomies that have vertically Michele 1979a, b, 1980, 1981, 1983a). The rec- elongate leaf cushions. Certain "minor" attri- ognition of an additional genus, segregated butes of cushion morphology allow the L. acu- from Lepidodendron, will largely complete the leatum-L. hickii correlation. As a consequence, process of defining architecturally distinct, it is now possible to segregate other taxa from monophyletic genera of Pennsylvanian-age Lepidodendron that have anatomy and aspects of lepidodendrid lycopods. Two genera described leaf-cushion morphology different from those from compressions have yet to be described of L. aaileaium-L. hickii. This paper concerns one convincingly from petrifactions, Bothrodendron of these segregates. and Asolanus. Both of these may be subsumed by already recognized forms, or may be found ANATOMICALLY-PRESERVEDMORPHOTYPES to have distinctive structural organization. {GENERA) OF PENNSVLVANIAN AGE The anatomically-preserved Pennsylvanian- Diaphotodendton DiMichele, gen. nov.—TYPE: age lepidodendrida represent six distinct or- Diaphorodendron vASCulnre (Binney) ganizational plans. Stem organ-taxa can be cor- DiMichele, comb. nov. BASIONYM: Lepido- related with cone organ-taxa by two means, in dendron vasculare Binney, Quart. J. Geol. Soc. the absence of attachment. First, co-occurrence Lond. 18:106-112, pi. IV, figs. 1-5, 1862. in coal balls (concretions of structural peat from Binney described and illustrated only one coal seams) is particularly compelling if only specimen.—TYPE: Slides prepared from one species of lycopod stem and one kind of Binney specimen No, 3—SM M. 4318 a-e; lycopod reproductive organ are known from Sedgwick Museum, University of Cam- the coal deposit. Second, comparison of cone- bridge, Cambridge, England. Collection axis anatomy with various metric and anatom- locality; Bullion Mine, Spa Clough, Burn- ical aspects of stem anatomy and morphology ley, Lancashire, England. Stratigraphy: may indicate that the organs are parts of the Westphalian A {Lower Pennsylvanian), same natural taxon. The following architec- Lower Coal Measures, Lancashire, [Illus- tural groups have been recognized—(stem trations in Binney {1862) include SM M. names are given first, followed by reproductive 4318 a = pi. IV, figs. 2 and 3; SM M. 4318 structures): 1) Lepidophloios-Lepidostrohus old- b = pi. IV, fig. 4; SM M. 4318 c = pi. IV, hamiiis-LepidQcarpon, 2) Sigiilaria-Mazocar- fig. S.] pon, 3) Paralycopodites-Flemingites (Flemingites Description of genus. Diaphorodendron in- is a recent segregate from Lepidostrobus, see cludes lycopods with arborescent habit. Growth Brack-Hanes and Thomas 1983), 4) Sublepi- form is either an excurrent trunk bearing de- dophloios (no cone correlation yet possible), 5) ciduous lateral branches, or a columnar trunk, Ldpidodendron-Achlamydocarpon takhtajanii, 6) which at maturity terminated growth with a "Lepidodendron" {DiaphoTodendrQn)-Achlamydo- dendritic, synchronously determinate crown. carpon varius. The two species of cones included Branching is anisotomous. Leaf cushions are in the genus 4cWarnydocarpon, A. takhtajanii and vertically elongate on stems of all sizes; their A. varius, have no substantive anatomical sim- ornamentation is simple and may include shal- ilarities (DiMichele 1983a), so their placement low plications above or below the leaf scar. in this genus does not reflect close pbyloge- Parichnos are strictly foliar {confined to the leaf netic relationship. The congeneric status of A. scar, not present below the scar as infrafoliar takhtajanii and A. varius reflects certain organi- prints). The leaf scar is at or above the middle zational similarities that appear to have been of the cushion. The keel is relatively promi- attained independently; they represent similar nent, but the cushions are not "fleshy" (strong- "grades" of cone evolution in different lin- ly protruding). Interareas are present between eages. leaf cushions, as fissures or tangentially ex- Species from ail of these genera, except Sig- panded zones on stems with developed peri- illaria, have been included at some historical derm. The periderm is bizonate, with a thick point, often only by tradition, in Lepidodendron. phelloderm and thinner phellem. Phelloderm 1985J DiMICHELE: DEAPHORODENDRON 455 is composed usually of tangentially alternating Card. 39:263-288, 1952.—TYPE: Specimen layers of thicker- and thinner-walled ceii.s, es- No. WCB 781, and slides and peels thereof; pecially wei-i. developed in the larger speci- peels in Paleobotanical Collections, De- mens; the thinner-walled cells are often de- partment of Plant Biology, University of graded. Phellem is homogeneous and usually Illinois-Urbana. Emended description and resinous in appearance. As in most other lepi- further synonymy in DiMichele (1979b). dodendrid lycopods, the primary cortex ia three- Diaphorodendron phillipsii DiMichele, comb, zoned. The outer cortex is composed of radially nov. BASIONTYM: Lepidodendron phillipsii aligned areas of thicker- and thinner-walled DiMichele, Palaeontographica, Abt. B 171: cells (dictyoxylon), the thinner-walled cells 122-136, 1981.—TYPE: Specimen No. 9876, clustered around the leaf traces; the middle and and slides and peels thereof; Paleobotani- inner cortical zones are variable in character, cal Collections, Department of Plant Biol- but usually contain cells with dark contents, ogy, University of Illinois-Urbana, and the inner zone ia thin. The stele is usually a mixed protostele; however it may be a dis- tinctly medulla ted protostele with primary xy- DISCUSSION iem longitudinally dissected. Cones are borne Segregation of Diapkoradendran from Lepido- on protosteiic lateral branches, produced on dendron permits formal recognition that these axes usually <2 cm in diameter (cones there- two groups have distinctive morphologies. This fore terminal or subterminal). Leaf abscission also results in a more narrow morphological and secondary xylem occur. circumscription of Lepidodendron, which may Stems of the type described here co-occur now constitute a monophyietic ("natural") with cones of the Achlamydocarpon varius-type: group. The anatomical characteristics of true (Taylor and Brack-Hanes 1976; Leisman and Lepidodendron are described and illustrated by Phillips 1979), which bear Cappasporites micro- Watson (1907) and DiMichele (1983a) in de- spores (Courvoiaier and Phillips 1975) and Cys- scriptions of Lepidodendron hickii, the only de- tosporites varius megaspores. Diapkorodendron scribed species of petrifaction lepidodendrid stems probably were attached to root systems with leaf cushions like those found on Lepido- of Stigmaria. This is inferred from Stigmaria with dendron aculeatum and similar forma. The major the distinctive periderm architecture character- characteristics of Lepidodendron and Diaphoro- istic of DiaphorodendroH stems; such Stigmaria dendron are contrasted in table 1. In final con- may occur in coals containing one or more sideration, the anatomy of true Lepidodendron is species of Diapkoradendran. much more like that of Lepidophloios (DiMichele Etymology. The name Diaphorodendron ia de- 1979a) than it is like that of Diaphorodendron, rived from the Greek words diaphoros (differ- accentuating the inadequacy of leaf-cushion ent) and dendron (tree). It is neuter. shape as the basis for recognizing true Lepido- dendron. Additional new combinations. Lepidodendron historically has included many Diaphorodendron scJeroticum (Pannell) Di- morphologically distinctive forms on the basis Michele, comb, no v. BASIONYM: Lepido- of higher-than-wide leaf cushions in which the dendron sderoticum Pannell, Ann. Missouri leaf scar is above the vertical midpoint of the Bot, Card. 29:245-273, 1942.-TYPE: cushion. This leaf-cushion construction ap- LECTOTYPE, designated herein, Specimen pears to be the ancestral (plesiomorphic) state No. WCB 56, and slides and peels thereof. in the Lepidodendrales on the basis of com- PARATYPE, Specimen No. WCB 55, and parison with a number of different lycopod slides and peels thereof. Both specimens outgroups (DiMichele 1983b; DiMichele and housed in Paleobotanical Collections, Uni- Young in prep.). Thus, the level of appUcabil- versity of Connecticut, Storrs, Connecti- ity, or universality, of this character state lies cut. at or somewhere above the Lepidodendrales in the taxonomic hierarchy, so far as can now be Diaphorodendron dicentricam (Felix) Di- determined. The major lepidodendrid genera Michele, comb. nov. BASIONVM: Lepidoden- {architecturally distinct organizational plans) dron dicentricum Felix, Ann. Missouri Bot. appeared during the Lower Carboiiiferous 456 SYSTEMATrC BOTANY [Volume 10

TABLE 1. Comparative morphology of selected features of Uiapkorodendron and Lepidod^ftdron.

OrAPHORODENDRON LEPIDODENDRON Pith Mixed parenchyma and tracheids or uni- Uniformly parenchymatous to bizonate formly parenchymatous with an inner core of hypha-like paren- chyma Primary xylem Protostele or ring of tracheidal tissue Continuous ring of tracheidal tissue with longitudinal parenchymatous partings Protoxylem Exarch, distributed uniformly around Exarch, clustered into blunt points at mar- margin of primary xylem gin of primary xylem Cortex Three zoned Three zoned Inner Narrow, may contain cells with dark con- Narrow, may contain cells with dark con- tents, may partially ensheath leaf trace tents into middle cortex Middle Composed of thin-waUed parenchyma, Composed of thin-walled parenchyma, usually degraded usually degraded Outer Broad; composed of alternating radial Broad; composed uniformly of thick-walled bands of thicker- and thinner-walled parenchyma, or bizonate, with paren- cells that anastomose vertically; each chyma of outer zone containing dark thin-walled band encloses a Leaf trace contents Periderm Bizonate; inner zone (phelloderm) thick- Massive, homogeneous to bizonate, with- est, composed of tangentially alternat- out a clear phellem-phelloderm distinc- ing thick-walled and thin-walled cells; tion; cell-files tangentially expanded in outer zone (phelLem) homogeneous, the outer part of larger stems the cells often have resinous appear- ance Leaf-cushion Relatively shallow ligule pits; leaf trace Relatively deep ligule pits; leaf trace 'S'- anatomy straight, with nearly horizontal path shaped Cones Achlamydocarpon varius Achlatnydocarpon takhtajanii Microspores Capposporites ILycospora

{Meyer-Berthaud 1984), In. some cases these ly- compression specimens, encompasses both true copods retained the ancestral leaf-cushion shape lepidodendron and Diaphorodendton. Differen- at some stage in their development, as in the tiating these genera in compression-impres- genera considered in this report; in other cases sion preservation is likely to be more difficult leaf-cushion shape was among the divergent than in anatomical preservation. Considerable characters, as in Lepidophloios, Wider-than-high progress has been made by Thomas (1970) in leaf cushions are an apomorphic (derived) state attaining a clearer delimitation of compression that distinguishes Lepidophloios from those forms species of LepidodendroH sensu lato. However, that retained the ancestral state of this one findings from anatomy only recently have been character. Those taxa retaining the ancestral applied to compressions (DiMichele 1983a; state are not necessarily allied more closely to Wnuk 1985), and the acceptability and util- each other than any one may be to Lepido- ity of conclusions drawn from these studies has phloios, since they diverge from each other in yet to be evaluated. As mentioned above, other morphological aspects. Because the na- compression fossils of lycopods display a very ture of the evolutionary process is one of di- limited range of morphological characters, es- vergence from ancestral form, creation of taxo- pecially in fragmentary specimens. Because of nomic groups based only on ancestral characters this, DiapkariidendraH may be recognizable more does not recognize that evolutionary diver- by its lack of those leaf-cushion characters that gence in other traits has occurred and new ar- distinguish Lepidodendron than by unique fea- chitectures arisen. Such characters cannot de- tures of its cushion architecture {this is not to limit "natural" taxa. say that Diaphorodendron lacks other derived Lepidodendran, as it is presently appUed to traits). 1985] DiMICHELE: DIAPHORODENDRON 457

As I aow understand the problem, true Lep- (N.H,), and Dr. David Price, Sedgwick Museum, Uni- idodendron may be recognized in compresaion- versity of Cambridge, were instrumental in location impression preservation by the combination of of the type specimens of Lepidodendron vasculare. Dr. the following characters: leaf-cushion height to William Crepet, University of Connecticut, located width ratios greater than, equal to, and occa- the type specimens of hepidodmdron scleraticum. This work was supported in part by a grant from the NSF sionally less than one {ratios close to one ap- (DEB-8210475). parently occur on small stems of all species, and are the rule in other species on stems of LITERATURE CITED all diameters); leaf cushions raised or radially- BRACK-HANES, S. D. and B. A. THOMAS. 1983, Areex- thick, sometimes with barred (deeply plicate) amination of Lepidastrobu^ Brongniart. Bot. J. Linn. lower keels; ontogeny of individual cushions Soc. 86:125-133. poasibly iaometric, at least in early stages COURVOKIER, J. M. and T. L. PHILLEPS. 1975. Corre- (DiMichele, Pfefferkorn, and Gillespie in prep.); lation of spores from Pen nsy Ivan ian coal-ball infrafoliar parichnos present below leaf scar; fructifications with dispersed spores. Micropa- leaf cushions maintained on large-diameter leontology 21:45-59. stems by expansion of sub-epidermal cells and DIMECHELE, W. A. 1979a. Arborescent lycopods of Pennsylvanian age coals: Lepi^iopkloLas. Palaeon- limited development of interareas, thus large tographica, Abt. B 171:57-77. diameter stems have closely spaced, large leaf •——-. 1979b. Arborescent lycopods of Pennsyl- cushions; branching largely isotomous, except vanian age coals: Lepidodendron dicmtricutn C. Fe- for the production of cones, which are borne lix, PaLaeontographica, Abt. B 171:122-136. on small lateral branches {halonial branches) • . 1990, Paralijcapadites Morey & Morey, from produced by aniaotomy. In contrast, Diaphoro- the Carboniferous of Euramerica—A reassess- dindran leaf cuahions are generally simple. The ment of the generic affinities and evolution of limited capacity of stem interarea expansion "Lepidodendron" brevifaUum Williamson. Amer. J. caused the cushions, ultimately, to be sloughed Bot. 67:1466-1476. from the stem surface. The following criteria, . 1981. Arborescent lycopods of Pennsylva- however unorthodox in light of traditional nian age coals: LepiAadendron, with description of a new species. Palaeontographica, Abt. B 175:85- usage, may allow this genus to be recognized 125. in compression: leaf cushions generally small; , 1983a. Lepidodmdron hicHi and generic de- cushion height greater than width on stems of limitation in Carboniferous lepldodendrld ly- all diameters; cushions relatively flat, protrud- copods. Syst. Bot. 8:317-333. ing little from the stem surface; ontogeny of 1983b. Timing and controls of diversifica- individual cushions probably allometric; infra- tion in the Carboniferous Lepldodendtales foliar parichnos lacking; interareas develop but (Abst.). Amer. J. Bot. 70(5, part 2);70-71. cushions ultimately sloughed from surfaces of LEISMAN, G. L. and T. L. PHILLIPS, 1979. Megaspo- larger stems; branching mostly anisotomous. rangiate and microsporangiate cones of Achla- mydocarpon varius from the Middle Pennsylva- Compressions with higher-than-wide leaf nian. Palaeontographica, Abt. B 168:100-128. cushions must be recognized as encompassing MEVER-BERTHAUD, B. 1984. Les axes de lycophytes a more than Lepidodendron; otherwise the genus structure anatomlque conservee du Carbon if ere becomes a polyphyletic group, and will, con- Basal (Tournasien) de la Montague Noire: Trabi- sequently, be of limited use in phylogenetic caulis gen. nov, et tandeyrodendron gen. nov. Pa- and evolutionary analyses. Recognition of this laeontogtpahlca, Abt. B 190:1-36. problem is the first step toward its solution, SCOTT, D. H. 1906. On the structure of Lepidodendron which will be determined in final analysis by obavatum Sternb. Ann. Bot. (London) 20:317-319. the names that are uaed in floristic and taxo- SEWARD, A, C. 1906. The anatomy of Lepidodendron nomic studies. anuleatum Sternb. Ann. Bot. (London) 20:371-381. TAYLOR, T. N. and S. D. BRACK-HANES. 1976. Ackla- ACKNOWLEDGMENTS. I would like to thank the fol- mydocarpon varius comb, nov.: Morphology and lowing people for helpful comments on the manu- reproductive biology. Amer. J. Bot. 63:1257-1265. script; Porter P. Lowry II, Missouri Botanical Garden, THOMAS, B. A. 1970. Epidermal studies In the Inter- Dr. Christopher Wnuk, United States Geological Sur- pretation of Lepidodendron species. Palaeontology vey, Dr. Robert A. Gastaldo, Auburn University, Dr. 13:145-173. Tom L, Phillips, University of Illinois and two anon- WATSON, D. M. S. 1907. On a confusion of two ymous reviewers, Mr. Cedric Shute, British Museum species {Lepidodendron harcotirtii Witham and L. 458 SYSTEMATIC BOTANY [Volume 10

hkkii sp. nov.) under Lepidodendron harcaurtii the Bernice Basin, Sullivan County, Pennsylva- Witham in Williamson's XIX Memoir, with a de- nia. PalaeontographLca, Abt. B 195:153-181. scription, of L. kiikii sp. nov. Mem. Proc. Man- chester Lit. Soc. 49: MemoijT 13, 22 pp. Current address-. Department of Paleobiology, Na- WNUK, C. 1985. The ontogeny and paleoecology tional Museum of Natural History, Smithsonian In- of Lepidodetidron rimosum and Lepidod^tidroti br^- stitution, Washington, DC 20560. lonens£ trees from the Middle PennsyIvanian of

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