Rudolph Serbet

Characterizing the Most Primitive Seed Ferns. I. A Reconstruction of Elkinsia polymorpha

Abundant gymnospermous remains occur in association with Elkinsia polymorpha in Upper Devonian deposits near Elkins, West Virginia, and these provide an opportunity to characterize and further refine our concepts of the most ancient seed ferns. The sporophyte of E. polymorpha has helically arranged dimorphic fronds, with large numbers of either preovulate cupules or synangiate prepollen organs borne terminally on the fertile fronds. Vegetative fronds are planar, with rachides that fork up to four times, and pinnate laterals that terminate in sphenopterid pinnules. Fertile fronds branch dichotomously throughout and are three-dimensional in the distal regions. Stems display a centrarch, three-ribbed protostele with prominent sclerenchyma of the sparganum type in the outer cortex. The frond rachis is vascularized by two C-shaped bundles. The hydrasperman preovulate cupules are as characterized in earlier studies. Prepollen organs consist of six to eight radially arranged sporangia that are fused at the base and free distally. Elkinsia polymorpha is the first seed fern to be reconstructed from Devonian sediments and the first preovulate seed fern to be characterized as a plant. As such, it represents an important evolutionary unit for ongoing phylogenetic studies of the origin of seed plants.

Osmunda cinnamomea (Osmundaceae) in the upper Cretaceous of Western North America : Additional evidence for exceptional species longevity among filicalean ferns

The discovery of numerous anatomically preserved fossils in Upper Cretaceous sediments reveals that essentially modern osmundaceous ferns have inhabited southern Alberta, Canada, since the end of the Mesozoic. The Cretaceous fossils consist of small stems that are surrounded by leaf bases and adventitious roots. All of the features of the fossils fall within the ranges of variation for characters of living Osmunda cinnamomea L., and the fossils display all of the specifically diagnostic anatomical characters for this species. These include an ectophloic, dictyoxylic solenostele that lacks leaf gaps in the phloem, C‐shaped frond traces, frond bases with lateral stipular expansions, features of the endodermis, and disposition of sclerenchyma tissues in the stem and frond bases. A reexamination of extant specimens and of previously described fossils from Neogene and Paleocene deposits clarifies the range of variation for specifically diagnostic characters and reveals the more or less continuous presence of O. cinnamomea L. in western North America for at least 70 million years. This article provides an additional example of a well‐characterized fossil filicalean fern that can be confidently assigned to a species with living representatives. It is becoming increasingly clear that species longevity for homosporous pteridophytes can be far greater, and species turnover may be far lower, than expected from evolutionary models developed for flowering plants.

Triassic floras of Antarctica: Plant diversity and distribution in high paleolatitude communities

ABSTRACT Continental Triassic sequences in Antarctica are among the most continuous and best represented in Gondwana. Triassic fossil plants have been collected sporadically from Antarctica since the beginning of the twentieth century, but our knowledge of the vegetation during this time has dramatically increased during the last three decades. Here we review the fossil record of Triassic plants as representatives of natural groups from sites along the Transantarctic Mountains, using the fossils as evidence for successive vegetational changes through the Triassic, taking into account that these plant communities were living under particular high-latitude (70° or higher) paleoclimatological conditions, including a polar light regime. Even though our knowledge of the Triassic floras of Antarctica is still incomplete, this survey shows that these floras were remarkably diverse. Lycopsids, equisetaleans, ferns, seed ferns, ginkgoaleans, and conifers were major components of the landscape in Antarctica during this time. The diversity of gymnosperms is exceptional, with almost every major clade of seed plants present, despite the high paleolatitude; however, each clade is often represented by only one or a few genera. The occurrence of permineralized peat, along with compression-impression floras, has increased our knowledge of the morphology, reproductive biology, and evolution of many of the plants in these floras. In general, floral changes in Antarctica during the Triassic can be recognized elsewhere in Gondwana, especially in South America, although a strict correlation based on macrofossils is still not possible. Thus, this contribution represents the first attempt to bring together information on Triassic floras from continental Antarctica (excluding the Antarctic Peninsula) within a biostratigraphic framework and thereby to compare these floras with those from lower latitudes.

Systematics and Paleoecology of a New Peltaspermalean Seed Fern from the Triassic Polar Vegetation of Gondwana

A new Triassic seed fern is described on the basis of a large collection of well-preserved plant compressions from the Upper Triassic of Mt. Falla, Queen Alexandra Range, central Transantarctic Mountains. The foliage is simple entire-margined to pinnatifid to partly pinnate and is assigned to Dejerseya lobata (Jones et de Jersey) Herbst emend. nov. Associated with these leaves occur two new reproductive structures. The ovulate organ Matatiella dejerseyi sp. nov. is a lax, conelike structure with primarily shield-shaped megasporophylls that are dissected into three to four narrow lobes, each bearing a single recurved, naked ovule. The pollen organ Townrovia polaris sp. nov. consists of a slender axis arising from a covered reproductive bud, bearing pinnately arranged, stalked, elongate receptacles each with ∼20 unilocular, clavate pollen sacs; the pollen is bisaccate nontaeniate with an irregular longitudinal sulcus and coarse saccus endoreticulations, corresponding to the dispersed pollen Falcisporites australis. Similar pollen grains occur in the micropylar canals of seed cuticles of M. dejerseyi. Co-occurrence data indicate that the three taxa are probably different organs from one plant species. This new seed fern is assigned to the Matatiellaceae, which we place into the Peltaspermales because of structural similarities with vegetative and reproductive organs of other peltaspermalean seed ferns. It appears that several Triassic Gondwanan plant fossil taxa of currently uncertain affinities—such as Pachydermophyllum, Linguifolium, Carpolithus mackayi, and Andersonia—may belong to the Matatiellaceae as well. We suggest that the matatiellacean peltasperms were opportunistic, early successional plants that were particularly successful in colonizing stressed wetland environments in polar latitudes during the Triassic.

Taxodiaceous pollen cones from the Upper Cretaceous (Horseshoe Canyon Formation) of Drumheller, Alberta, Canada

Abstract One hundred permineralized cones, 1.0–1.2 mm × 1.5-2.0 mm, some attached to branching systems, have been examined from the Upper Cretaceous ironstones in the Horseshoe Canyon Formation near Drumheller, Alberta. Cones are borne laterally and terminally on specialized shoots. Microsporophylls are helically arranged on the cone axis with one large resin canal and two pollen sacs per microsporophyll. Pollen is 12–16 μm in diameter with one exit papilla that forms a low protuberance on the grain. External surfaces of grains are scabrate with numerous orbicules and macrogranules while the nexine is laminated. Arrangement of cones on branches is similar to those of Taxodium whereas the number of pollen sacs per microsporophyll is similar to Sequoia and Sequoiadendron . Pollen morphology is similar to Metasequoia and Taxodium , while ultrastructurally it most closely resembles that of Metasequoia . This combination of morphological features is unlike that found in any living taxodiaceous genus. These remains are therefore described as Drumhellera kurmanniae gen. et sp. nov. This study reveals the importance of whole plant reconstructions of other fossil Taxodiaceae due to the scarcity of distinctive morphological characters in isolated organs. Furthermore, the large number of fossil plant specimens associated with these taxodiaceous remains in the Horseshoe Canyon Formation show enormous potential for reconstructions of several types of seed plants.

Cunninghamia taylorii sp. nov., a Structurally Preserved Cupressaceous Conifer from the Upper Cretaceous (Campanian) Horseshoe Canyon Formation of Western North America

The fossiliferous ironstone deposits of the Upper Cretaceous Horseshoe Canyon Formation in the Drumheller badlands, Alberta, Canada, contain a diverse, anatomically preserved flora. Within this assemblage occur abundant stems, leafy shoots, leaves, ovuliferous cones, and pollen cone clusters that are here described as a new species of Cunninghamia. The stems have persistent leaf bases and plagiotropic branching. Some stems show several growth increments, and the cortex and pith are made up of resin canals, large parenchymatous cells, and lysigenous cavities. Leafy shoot axes have parenchymatous cells, resinous cells, lysigenous cavities, and resin canals within the cortex and pith. The leaves are helically arranged, lanceolate to falcate, with two abaxial stomatal bands, a large central resin canal, and two smaller lateral canals. The ovuliferous cones have numerous helically arranged bract scale complexes. The bracts and three-lobed ovuliferous scale are variously ornamented. Anatomical features of bracts include a well-defined hypodermal layer and resin canals with adaxial traces. A single vascular trace enters the complex and divides to produce the ovuliferous-scale trace and bract traces. Ovules/seeds are ovoid and weakly winged. The pollen cone–bearing branch apices show stalks of at least 17 pollen cones arranged in a pseudowhorl. Each stalk consists of an inflated base surrounded by 5–6 scale-like leaves. The anatomy and morphology of the fossil material agrees so closely with that of modern Cunninghamia that we are confident in describing it as a new species of this genus, Cunninghamia taylorii sp. nov. The present material provides a rare opportunity to contribute toward a better understanding of the specific variation, biology, ecology, and evolutionary history of cunninghamioid Cupressaceae.

Anatomically Preserved Ferns from the Late Cretaceous of Western North America: Dennstaedtiaceae

Rhizomes and stipe bases of dennstaedtiaceous ferns occur within a rich assemblage of permineralized plant fossils in the Upper Cretaceous Horseshoe Canyon Formation of southern Alberta, Canada. Two dennstaedtiaceous species are represented by procumbent rhizomes that branch frequently and produce closely spaced fronds. The dorsiventral rhizomes produce fronds from the top and sides and produce adventitious roots from the lower surface. Both species are assigned to the morphogenus Microlepiopsis gen. nov. on the basis of distinctive solenostelic rhizomes, with sclerenchymatous pith and cortex and relatively simple frond trace anatomy. In one species, Microlepiopsis bramanii sp. nov., the trace diverges as two \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

Anatomically Preserved Ferns from the Late Cretaceous of Western North America. II. Blechnaceae/Dryopteridaceae

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