STUDIES OF PALEOZOIC FERNS: TUBICAULIS STEWARTII SP. NOV. AND EVOLUTIONARY TRENDS IN THE GENUS

Eggert , Donald A. (Yale U., New Haven, Conn.) Studies of Paleozoic ferns: Tubicaulis stewartii sp. nov. and evolutionary trends in the genus. Amer. Jour. Bot. 46(8): 594–602. Illus. 1959.—Tubicaulis stewartii, a new species of the order Coenopteridales is described. The specimen was derived from the Upper Pennsylvanian of Berryville, Illinois, and is characterized by having a lacunar middle cortex, a well-developed integumentary system bearing uniseriate hairs, and xylem parenchyma organized into vertically anastomosing strands. In addition, multiseriate (somewhat transitional to reticulate) bordered pitting is present in the petiolar metaxylem elements, while those of the stem stele are multiseriate scalariform. The habit is intermediate between that of a form such as Osmunda and a tree fern, having an upright tapering stem which gives off prominently decurrent petioles in a 2/5 divergence. A reinvestigation of the type specimen of the most closely allied species, T. multiscalariformis, of Upper-Middle Pennsylvanian age, has shown that it has similar features in the cortex, metaxylem, and integumentary layers. Tubicaulis multiscalariformis and T. stewartii form a distinct group in the 6 species now known, whose evolution has most likely involved the retention of a more primitive form of pitting (multiseriate scalariform) with parenchymatization of the xylem. The remaining species of the genus have not developed xylem parenchyma but have developed circular bordered pitting. The relationships of the genus to other genera in the Coenopteridales remain obscure.     

STUDIES OF PALEOZOIC FERNS: THE FROND OF ANKYROPTERIS GLABRA

Eggert , Donald A. (Southern Illinois U., Carbondale.) Studies of Palerzoic ferns: The frond of Ankyropteris glabra. Amer. Jour. Bot. 50(4): 379–387. Illus. 1963—The major features of the frond of A. glabra are described on the basis of preserved parts found in Middle Pennsylvanian coal ball material from Illinois. The frond is planated and has well-developed foliar laminae. Primary pinnae arise from the petiole in 2 alternating series, and secondary pinnae arise in a similar fashion from the primary pinnae. Foliar laminae occur on the secondary pinnae and have dichotomous venation. The xylem of the petiole has a diupsilon configuration in the lower part of the axis, while higher in the petiole the xylem forms a strand resembling that of the European species A. westfaliensis. The xylem strands of the primary pinnae arise from the adaxial antennae of the petiolar vascular strand as somewhat C-shapcd bodies and develop antennae and become H-shaped at higher levels. A gap occurs in the antenna of the petiole vascular system above the level of departure of the primary pinna trace. Terete vascular strands occur in the secondary pinna axes which arise from the adaxial antennae of the xylem of the primary pinnae. The foliar laminae are relatively thin, have an irregular outline, and their histology is like that found in many living ferns. The frond of A. glabra illustrates that leaf evolution had progressed in at least one species of the coenopterid family Zygopteridaceae to the extent that an essentially 2-dimensional frond of modern aspect, and with well-developed foliar laminae, was present by Middle Pennsylvanian time.     

KLEINODENDRON AND XYLEM ANATOMY OF CLUYTIEAE (EUPHORBIACEAE)

Kleinodendron, a new genus of Euphorbiaceae, was assigned by Smith and Downs to the tribe Cluytieae. A xylem anatomical survey indicates that there are no objections to this placement. Woods of Cluytieae are diverse but may be characterized generally by having pores which average less than 80 μ in diameter and which are well divided between solitary and radial multiple distributions in the same species; simple vessel perforations; alternate intervascular pitting; fiber-tracheids and libriform wood fibers; exclusively uniseriate, or uniseriate and biseriate heterocellular vascular rays in the same species; uniseriate “bridges” linking superposed biseriate ray segments; diffuse, diffuse-in-aggregates, and scanty vasicentric axial parenchyma, sometimes in the same species; and crystal rhomboids. That Microdesmis and Pogonophora diverge sharply from these generalizations in having scalariform vessel perforations and broad vascular rays, is an indication that they may not be closely related to other genera in Cluytieae.     

BOSTONIA PERPLEXA GEN. ET SP. NOV., A CALAMOPITYAN AXIS FROM THE NEW ALBANY SHALE OF KENTUCKY

Bostonia perplexa, gen. et sp. nov., was collected from the Lower Mississippian Falling Run member of the Sanderson Formation. The single short segment of an axis, preserved as a petrifaction, contains at least three vascular columns, each with both primary and secondary tissues. Primary xylem is two or three ribbed, and contains several mesarch protoxylem strands. Gymnospermous secondary xylem is characterized by both uniseriate and multiseriate rays. The ground tissue is parenchymatous except for a few clusters of sclerotic cells. In its apparent polystelic nature, the specimen superficially resembles members of the Pennsylvanian to Permian Medullosaceae. All evidence currently available, however, leads to the conclusion that this species should be placed in the Upper Devonian to Lower Mississippian Calamopityaceae. It has not been determined with certainty whether the species is polystelic (in the sense of the Medullosaceae), or whether the apparent polystely is the result of stelar branching proximal to the level of branch divergence.     

ANATOMY AND AFFINITIES OF PENTHORUM

The genus Penthorum L. consists of two species of perennial herbs, P. sedoides of eastern North America and P. chinense of eastern Asia. Penthorum has long been considered intermediate between Crassulaceae and Saxifragaceae. An anatomical study of both species was undertaken to contribute to a better understanding of the relationships of these plants. Prominent anatomical features of Penthorum include: an aerenchymatous cortex and closely-spaced collateral vascular bundles of stems; one-trace unilacunar nodes; brochidodromous venation, rosoid teeth bearing hydathodes, and anomocytic stomata of leaves; angular vessel elements with many-barred scalariform perforation plates and alternate to scattered intervascular pits; thin-walled non-septate fiber-tracheids; abundant homocellular erect uniseriate and biseriate rays; and absence of axial xylem parenchyma. In general, Penthorum possesses neither the morphological nor the anatomical synapomorphies which define Crassulaceae, and features shared with Saxifragaceae are largely symplesiomorphous. Thus Penthorum is probably best classified in the monogeneric Penthoraceae.     

ELECTRON MICROSCOPY OF WOOD OF CALLIXYLON AND CORDAITES

Replicas and ultrathin sections of the wood of two Paleozoic genera, Callixylon and Cordaites, were examined with the electron microscope. The pattern of wall layering of Callixylon closely resembles that of extant plants. An electron-dense compound middle lamella markedly thickened at the corners of cells, a thin, electron-transparent S₁ layer of the secondary wall, and a thick, electron-dense, partially decayed S₂ layer of the secondary wall are evident in transverse sections of tracheids. No S₃ layer seems to be present. The structure of the bordered pit-pairs of Callixylon is described in detail. The slitlike outer pit apertures are conspicuously narrower and shorter than the inner pit apertures. Both sections and replicas of the bordered pit-pairs display pit membranes lacking tori. Microfibrillar structure is obscure in both sections and replicas of Callixylon wood. Replicas of the bordered pits of Cordaites wood are very similar to those of Callixylon. Pit membranes lack tori, and microfibrillar structure is not very discernible. Knowledge about the evolution of the torus is summarized. It is postulated that the type of pit membrane of Callixylon and Cordaites, which is very homogeneous in structure and lacks a torus, represents a primitive condition among gymnosperms from which structurally more complex pit membranes and the torus later evolved.     

AN UNUSUAL BOTRYOPTERID SPORANGIAL AGGREGATION FROM THE MIDDLE PENNSYLVANIAN OF NORTH AMERICA

A new fertile species of Botryopteris (Botryopteridaceae: Filicales) is described from four incomplete Middle Pennsylvanian specimens. Fertile pinnae of B. cratis sp. n. consist of branched frond members bearing numerous globose sporangia. Surrounding the sporangial aggregations are larger sterile frond members (0.5-1.5 mm diam). Fertile pinnae are oval in transverse section and possess an eccentrically developed cortex composed chiefly of fibers. Some frond members show the typical botryopterid xylem configuration with three protoxylem strands. Spherical sporangia are loosely aggregated on the smallest pinnae by short, broad stalks. The annulus is band-like, two cells high, and extends transversely across the lower half of the sporangium for approximately half the circumference. Spores are oval, trilete, verrucate, and covered by a thin separable layer. Sporangium morphology is like that of Botryopteris antiqua, but the spores closely resemble those of B. globosa. The new species is unlike previously described fructifications of Botryopteris in exhibiting a small pinna system which surrounds smaller pinnae bearing sporangia in an aggregation. The new form is considered to be less specialized than previously described globosoid forms because the sporangia are much less crowded. Isolated frond members, believed to belong to the new species, have a large central arm in the pinna xylem trace that resembles the Stephanian taxon B. renaultii. Small stems attached to the adaxial surface of frond members are radial, protostelic, centrarch, and have a three-zoned cortex. The inner cortical zone contains large elongate cells with distinctive layered deposits. Stems are covered with uniseriate multicellular hairs on multicellular bases. Stems compare closely with B. mucilaginosa in histological features.     

THE VEGETATIVE ANATOMY OF SCHOPFIASTRUM DECUSSATUM FROM THE MIDDLE PENNSYLVANIAN OF THE ILLINOIS BASIN

Schopfiastrum decussatum, a monostelic pteridosperm, has been recovered from Middle Pennsylvanian age coal balls from six localities within the Illinois Basin. Additional features of stem anatomy include the presence of horizontal sclerotic plates in the inner cortex, secretory ducts in the inner and outer cortex, and adventitious roots. The primary xylem is interpreted as bilobed, emitting massive leaf traces in a distichous manner. Five orders of frond members are described, including pinnules. All orders of the frond contain secretory ducts and tissues characteristic of Schopfiastrum stems. The rectangular, bilobed protostele, and method of leaf trace origin indicate that Schopfiastrum is more closely related to certain lower Carboniferous seed ferns than to contemporary Pennsylvanian pteridosperms.     

Charred wood of Prototaxoxylon from the Wuchiapingian Wutonggou Formation (Permian) of Dalongkou,northern Bogda Mountains,northwestern China

Charred wood occurs sporadically in sedimentary rocks in China. A marcroscopic charcoal with well-preserved anatomical structure is described from the Wuchiapiangian Wutonggou Formation in the southern part of Dalongkou section, northern Bogda Mountains in the Junggar Basin, northwestern China. It is characterized by uniseriate radial tracheidal pitting, taxaceous tertiary spiral thickenings in the tracheidal walls, uniseriate tangential tracheidal pitting, homogeneous, uniseriate, 2–10 cells high xylem rays, and 1–2 pits in each cross-field. It is assigned to Prototaxoxylon uniseriale Prasad. The uniseriate, bordered, contiguous, rarely separate tangential pitting of P. uniseriale is evidenced clearly for the first time. The features of this species show a close affinity with conifers. The coniferous charred wood may have been derived from an extrabasinal forest, perhaps from upland environment deep within the hinterland, according to results of modern taphonomic research.     

LEAF TRICHOMES OF SOME PARTHENIUM SPECIES

Guayule (Parthenium argentatum), a native shrub of the Chihuahuan desert, contains rubber. Guayule has been crossed with other Parthenium species in an attempt to improve its agronomic characteristics. The resulting hybrids show intermediate morphologies. Each Parthenium species has a characteristic combination of leaf trichomes. In order to recognize the contribution of each parent in future studies of hybrids, characteristics of leaf trichomes of the following Parthenium species were studied: P. tomentosum, P. fruticosum, P. Schottii and P. rollinsianum. All species studied had two or more types of trichomes, and, in some species, trichomes of upper and lower epidermal surfaces were different. The prominent trichomes on upper epidermis of P. tomentosum and P. fruticosum were simple, uniseriate, conical trichomes, which also were observed on both epidermal surfaces of P. Schottii. Extremely long, narrow, simple, whiplike, trichomes formed a dense cover on both surfaces of P. rollinsianum and on the lower surfaces of P. tomentosum and P. fruticosum. Simple, uniseriate, cylindrical trichomes, and biseriate, glandular trichomes were observed in all four species.     

Sclerospiroxylon xinjiangensis nov. sp., a gymnospermous wood from the Kungurian (lower Permian) southern Bogda Mountains,northwestern China: Systematics and palaeoecology

A new silicified wood, Sclerospiroxylon xinjiangensis Wan, Yang et Wang nov. sp., is described from the Cisuralian (lower Permian) Hongyanchi Formation in southeast Tarlong section, Turpan City, Xinjiang Uygur Autonomous Region, northwestern China. The fossil wood is composed of pith, primary xylem and Prototaxoxylon-type secondary xylem. The pith is solid, circular, heterocellular, with sclerenchyma and parenchyma. The primary xylem is endarch to mesarch, with scalariform thickenings on tracheid walls. The secondary xylem is pycnoxylic, composed of tracheids and parenchymatous rays. Growth rings are distinct. Tracheids have mostly uniseriate, partially biseriate araucarian pitting on their radial walls. Helical thickenings are always present on both the radial and the tangential walls. Rays are 2–14 cells high, with smooth walls. There are 2 to 7, commonly 2 to 4 cupressoid pits in each cross-field. Leaf traces suggest that S. xinjiangensis nov. sp. was evergreen with a leaf retention time of at least 15 years. Based on the sedimentological evidence, growth rings within the S. xinjiangensis nov. sp. could have been caused by seasonal climatic variations, with unfavorable seasons of drought or low temperature. Low percentage of latewood in each growth ring is probably due to the intensity of climatic seasonality and/or long leaf longevity.     

Wood, bark and stem anatomy of New World species of Gnetum

Quantitative and qualitative data are presented for 11 collections of six species. The wide range of character states for the species is presented in the form of a key to emphasize their potential systematic correlations. Distinctive among these are phcllem characteristics. Fibre-tracheids are newly reported for lianoid Gnetum species. Cells previously thought to be like companion cells in secondary phloem are shown to be uniseriate rays, counterparts to uniseriate xylem rays. Laticifers are abundant in most of the species, and are newly described for secondary tissues of Gnetum. Presence of tyloses in laticifers of two species is apparently a new report for vascular plants. Tori are present in two New World Gnetum species, adding to the report in African species. Perforation plates are simple except near or in primary xylem, where they are simple or foraminate. Torus presence and foraminate perforation plate presence are features more reminiscent of Ephedra and other gymnosperms than of angiosperms. The bark of Gnetum is also very similar to that of Ephedra.     

Wood anatomy of some trees with diffuse- and ring-porous wood: Some functional and ecological interpretations

Abstract

The xylem conduit dimensions (i.e. their width and length) have been measured in 1-year-old internodes, nodes and node-to-petiole (N-P) junctions of three species with diffuse-porous wood, namely Ceratonia siliqua L., Laurus nobilis L. and Olea europaea L. as well as of three species with ring-porous wood, namely Quercus ilex L., Q. suber L. and Q. pubescens Willd‥ The xylem conduit diameter and length distributions have been related to the drought resistance strategies adopted by the six species. C. siliqua and Q. ilex (drought avoiding water spenders) showed the widest xylem conduits (each species within its characteristic pattern of wood anatomy). This is consistent with their high demand of efficient water transport to leaves. L. nobilis (drought avoiding water saver) showed relatively narrow xylem conduits, efficient enough, however, to assure water supply to leaves at the reduced transpiration rate exhibited by the species. O. europaea, Q. suber and Q. pubescens (drought tolerants) showed the narrowest xylem conduits but also the longest ones. The xylem system of C. siliqua and Q. ilex represented a good compromise between efficiency and safety of the water transport, the former as due to wide xylem conduits, the latter to the reduced xylem conduit length as well as to the strong «hydraulic constrictions» at their nodes and N-P junctions. The ecological interpretation of such hydraulic architecture is discussed.     

ANATOMICAL STUDIES OF CYATHEA AND TRICHIPTERIS (CYATHEACEAE)

Comparative anatomical studies of the mature stems of two species each of Trichipteris and Cyathea (Cyatheaceae) are described. The outermost boundary of the stem is typically a two-layered hypodermis. Mucilage-sac cells are randomly distributed in all parenchymatous areas of the stem and form articulated laticifer systems. Localized areas of sclerenchyma tissue occur in the cortex of both T. microphylla and C. suprastrigosa. All species studied possess medullary bundles, whereas cortical bundles are found only in T. trichiata. Accessory bundles occasionally are associated with indentations in the internal stelar sheath of T. trichiata. The stelar pattern in each genus is a dictyostele and consists of individual meristeles. Distinctive cubical cells typically occur wherever sclerenchymatous fibers and parenchyma cells abut one another. Tangential cells occur within the primary phloem of each meristele, and occasionally within the larger accessory bundles. The primary xylem of the adventitious roots is typically diarch, although triarch and tetrarch xylem may occur. Leaf traces and petiole strands are similar anatomically to the accessory bundles. Based upon this study Trichipteris and Cyathea show striking anatomical similarities, and appear to be closely-related taxa.     

VEGETATIVE AND FERTILE STRUCTURES OF CYATHOTHECA VENTILARIA FROM THE UPPER PENNSYLVANIAN OF THE APPALACHIAN BASIN

Permineralized stems, leaves and a fertile structure assignable to Cyathotheca Taylor are described from the Late Pennsylvanian Duquesne Coal of eastern Ohio. The new material, C. ventilaria sp. nov., provides the first evidence of vegetative structures for the genus. Vegetative parts are referred to the fertile fragments based upon distinctive vascular morphology, common histological features, and close association. Stems are up to 5.0 mm in diam and have an apparently endarch dictyostele with scalariform metaxylem tracheids. Secondary xylem consists of tracheids with bordered pitting and uniseriate, parenchymatous rays 1–9 cells high. Leaves are arranged in a 3/8 pattern. They are small, pinnately-lobed, and vascularized by an U-shaped bundle. Distal to divergence, one of the apparent leaf traces becomes radial to resemble the base of a fertile structure. This implies a mode of attachment for the fructification and suggests evidence to interpret its homologies. The fertile specimen consists of laminae that diverge from a short stalk, and bifurcate distally. Laminae bear sporangia 0.6–0.7 mm in diam attached adaxially by vascularized pedicels. Spores average 36 μm in diam and are of the Kewaneesporites type. The combination of features now known for Cyathotheca exclude it from assignment to a currently-recognized major group of vascular plants, thus emphasizing that the Pennsylvanian coal swamp flora included a greater diversity than commonly is interpreted.     

THE MORPHOLOGY OF STIGMARIA STELLATA

Stigmaria stellata Goeppert is a lycopod underground system occurring in Upper Mississippian and equivalent age rocks of Europe and North America. This taxon has previously been based on impressions exhibiting radiating ridges and furrows around each lateral appendage scar and numerous polyhedral projections on the remainder of the axis. Anatomically preserved specimens from the Chester Series (Upper Mississippian) of Illinois reveal that the distinctive surface pattern of this species results from polyhedral wedges of thick-walled cells in the outer cortex. Decortication produces a smooth outer surface that is indistinguishable from that of the much more abundant Stigmaria ficoides. The structure of S. stellata is quite similar to the structure of other petrified stigmarians, but the following are some of the anatomical characters that distinguish it: (1) presence of abundant polyhedral wedges of thick-walled cells in the outer cortex; (2) absence of secondary cortex; (3) very tall rays associated with appendage traces that remain confluent with the secondary xylem to its outer margin; (4) the absence of a connective in the lateral appendages. The anatomical characters of Stigmaria stellata confirm it as a taxon of at least specific rank.     

What causes the differences in cavitation resistance of two shrubs? Wood anatomical explanations and reliability testing of vulnerability curves

Relationships between xylem anatomical traits and cavitation resistance have always been a major content of plant hydraulics. To know how plants cope with drought, it is extremely important to acquire detailed knowledge about xylem anatomical traits and assess the cavitation resistance accurately. This study aims to increase our knowledge in the methods determining cavitation resistance and xylem anatomical traits. We selected a semi-ring-porous species, Hippophae rhamnoides L., and a diffuse-porous species, Corylus heterophylla F., to clarify the reasons for the difference in cavitation resistance based on detailed xylem anatomical traits and reliable vulnerability curves (VCs). Both Cavitron and bench dehydration (BD) were used to construct VCs. Xylem anatomical traits, including pit membrane ultrastructure of these two species, were determined. The VCs obtained by the two different techniques were of different types for H. rhamnoides, its Cavitron VCs might be unreliable because of open-vessel artifacts. On the basis of BD VCs, H. rhamnoides showed higher cavitation resistance than C. heterophylla, and this is attributed to its low vessel connectivity as well as non-porous and thicker pit membranes.     

MOLECULAR PHYLOGENY OF DISCOSPORANGIUM MESARTHROCARPUM (PHAEOPHYCEAE) WITH A REINSTATEMENT OF THE ORDER DISCOSPORANGIALES1

A molecular phylogenetic analysis of the little‐studied filamentous brown alga Discosporangium mesarthrocarpum (Meneghini) Hauck using rbcL and partial 18S rDNA sequences revealed that the species forms a monophyletic clade with Choristocarpus tenellus (Kütz.) Zanardini that is sister to all other brown algae. Although D. mesarthrocarpum has unique disk‐shaped plurilocular reproductive organs, D. mesarthrocarpum and C. tenellus share the following basic morphological features, which are considered to be plesiomorphic characters in the brown algae: (1) apical (and diffuse) growth; (2) uniseriate, subdichotomously branched filaments; (3) multiple chloroplasts per cell without pyrenoids; and (4) lack of heterotrichy and of phaeophycean hairs. The rbcL DNA sequence of an Australian D. mesarthrocarpum specimen showed considerable deviation from Mediterranean and Macaronesian specimens. Therefore, the presence of a second species in the genus is suggested; however, the taxonomic treatment of this putative species is not pursued in the present report. Regarding the higher‐ranking systematic position of D. mesarthrocarpum, reinstatement of Discosporangiaceae and Discosporangiales is proposed, and the inclusion of Choristocarpaceae in the order is also suggested. Under short‐day and long‐day culture conditions at 15°C–25°C, Mediterranean D. mesarthrocarpum exhibited a direct type of life history, with a succession of uniseriate filamentous thalli bearing characteristic disk‐shaped plurilocular zoidangia, but thalli did not survive at 10°C and below.     

Interxylary cork of <Emphasis Type="Italic">Saussurea discolor</Emphasis> and <Emphasis Type="Italic">S. pygmaea</Emphasis> (Asteraceae)

The root anatomy of the subalpine to alpine plant species Saussurea discolor (Willd.) DC., and Saussurea pygmaea (Jacq.) Spreng., (Asteraceae) has been investigated by means of light and fluorescence microscopy on specimens of Austrian provenance. Both species develop a so called interxylary cork which mediates the splitting of the root into various strands. This phenomenon takes place in the secondary xylem and involves the development of a periderm separating the originally solid xylem cylinder. Interxylary cork is currently known from approximately 40 species of the Dicotyledones. This is the first report of this specific anatomical structure from the two studied species.     

LEAF HAIRS IN ENCELIA (ASTERACEAE)

Four different kinds of leaf hairs occur in Encelia species. These are unicellular-based and multicellular-based uniseriate hairs, moniliform hairs, and biseriate glandular hairs. The unicellular-based uniseriate hairs appear responsible for increased leaf spectral reflectance by species within the genus. In particular, it appears that elongation of the distal cell of the uniseriate hair is necessary for increased leaf reflectance.