Search

Rhizomorphic lycopsids constitute the most derived lycophyte clade and some of the world's best-known plant fossils. Arboreous taxa within the clade evolved independently of other nonlycophyte trees. Their rootstocks (rhizomorphs) have distinctive morphologies and anatomies and unusually canalized ontogenies, leading to debates regarding homology and functional morphology. Traditionally referred to form genus Stigmaria , rhizomorphs of arboreous genera are repeatedly isotomous, producing a helical rhizotaxy of abundant determinate appendages (rootlets). Regarded as leaf homologues, reexamination of fossil and living Isoetes "rootlets" suggests some shared genetic and morphological traits with true roots, while maintaining many leaflike phenotypic traits. This logic cannot automatically be extended to the radially symmetrical, rootlet-producing rhizomorph axes, which are inferred to combine developmental programs that distinguish root from shoot in nonlycophytes. Comparative embryogeny of several fossil genera plus Isoetes suggests shared ontogeny and heterochronically driven divergences. The first-formed microphylls and root support the juvenile plant until the rhizomorph is produced laterally as a sui generis organ that rapidly co-opts the role of the first-formed root, transitioning from radial to bilateral to radial symmetry. We reevaluate the conventional view that the rootlets were abscised, despite their superficial origin. Rootlets are common in areas of comparatively low resistance, which suggests low penetrating power. In addition to dissolved minerals, rootlets may have gathered soil CO2 for use within the rhizomorph and/or shoot system, and exposed upwardly directed roots may have been photosynthetic. In soil, rootlets improved anchorage, whereas in open water, largely hollow mature roots may have enhanced stigmarian system buoyancy and nucleated floating peat mats. Examination of hundreds of in situ stumps has failed to locate an uprooted specimen; hollowed-out dead stumps were conduits for materials into potentially dysoxic levels in the substrate. We cannot identify close modern analogues for the ecological role played by these unique trees. [ABSTRACT FROM AUTHOR]

Fossils constitute the principal repository of data that allow for independent tests of hypotheses of biological evolution derived from observations of the extant biota. Traditionally, transformational series of structure, consisting of sequences of fossils of the same lineage through time, have been employed to reconstruct and interpret morphological evolution. More recently, a move toward an updated paradigm was fueled by the deliberate integration of developmental thinking in the inclusion of fossils in reconstruction of morphological evolution. The vehicle for this is provided by structural fingerprints—recognizable morphological and anatomical structures generated by (and reflective of) the deployment of specific genes and regulatory pathways during development. Furthermore, because the regulation of plant development is both modular and hierarchical in nature, combining structural fingerprints recognized in the fossil record with our understanding of the developmental regulation of those structures produces a powerful tool for understanding plant evolution. This is particularly true when the systematic distribution of specific developmental regulatory mechanisms and modules is viewed within an evolutionary (paleo-evo-devo) framework. Here, we discuss several advances in understanding the processes and patterns of evolution, achieved by tracking structural fingerprints with their underlying regulatory modules across lineages, living and fossil: the role of polar auxin regulation in the cellular patterning of secondary xylem and the parallel evolution of arborescence in lycophytes and seed plants; the morphology and life history of early polysporangiophytes and tracheophytes; the role of modularity in the parallel evolution of leaves in euphyllophytes; leaf meristematic activity and the parallel evolution of venation patterns among euphyllophytes; mosaic deployment of regulatory modules and the diverse modes of secondary growth of euphyllophytes; modularity and hierarchy in developmental regulation and the evolution of equisetalean reproductive morphology. More generally, inclusion of plant fossils in the evo-devo paradigm has informed discussions on the evolution of growth patterns and growth responses, sporophyte body plans and their homology, sequences of character evolution, and the evolution of reproductive systems. [ABSTRACT FROM AUTHOR]

Anatomically preserved fossil gleicheniaceous fern remains in carbonate marine concretions from Vancouver Island, British Columbia, Canada support the development of a whole plant concept for an Eocene species of Gleichenia , and provide data to develop the first organismal concept for an extinct species of Gleichenia from the Cenozoic fossil record. New information for completing the plant reconstruction includes anatomically preserved pinnule fragments with attached radial exindusinate sori of six to seven annulate sporangia containing trilete spores. While the overall pattern of evolution within Gleicheniaceae remains incompletely understood because well-documented fossils from pre-Cretaceous deposits are inconsistently preserved, this organismal plant concept strengthens evidence that all diagnostic features of the family Gleicheniaceae were present, and that essentially modern species were well-established and diversifying during the Cretaceous and Paleogene. • First whole plant reconstruction of a Cenozoic species of Gleichenia. • Characterized by both external morphology and internal anatomy. • Evidence of stems, frond fragments, and sori of sporangia containing spores. • Essentially modern species of Gleicheniaceae evolved no later than the Paleogene. • Family Gleicheniaceae is inconclusively present in pre-Cretaceous deposits. [ABSTRACT FROM AUTHOR]

Background The origin of the Equisetum strobilus has long been debated and the fossil record has played an important role in these discussions. The paradigm underlying these debates has been the perspective of the shoot as node-internode alternation, with sporangiophores attached at nodes. However, fossils historically excluded from these discussions (e.g. Cruciaetheca and Peltotheca) exhibit reproductive morphologies that suggest attachment of sporangiophores along internodes, challenging traditional views. This has rekindled discussions around the evolution of the Equisetum strobilus, but lack of mechanistic explanations has led discussions to a stalemate. Scope A shift of focus from the node-internode view to a perspective emphasizing the phytomer as a modular unit of the shoot, frees the debate of homology constraints on the nature of the sporangiophore and inspires a mechanism-based hypothesis for the evolution of the strobilus. The hypothesis, drawing on data from developmental anatomy, regulatory mechanisms and the fossil record, rests on two tenets: (1) the equisetalean shoot grows by combined activity of the apical meristem, laying down the phytomer pattern, and intercalary meristems responsible for internode elongation; and (2) activation of reproductive growth programmes in the intercalary meristem produces sporangiophore whorls along internodes. Conclusions Hierarchical expression of regulatory modules responsible for (1) transition to reproductive growth; (2) determinacy of apical growth; and (3) node-internode differentiation within phytomers, can explain reproductive morphologies illustrated by Cruciaetheca (module 1 only), Peltotheca (modules 1 and 2) and Equisetum (all three modules). This model has implications - testable by studies of the fossil record, phylogeny and development - for directionality in the evolution of reproductive morphology (Cruciaetheca-Peltotheca-Equisetum) and for the homology of the Equisetum stobilus. Furthermore, this model implies that sporangiophore development is independent of node-internode identity, suggesting that the sporangiophore represents the expression of an ancestral euphyllophyte developmental module that pre-dates the evolution of leaves. [ABSTRACT FROM AUTHOR]

PREMISE OF THE STUDY: Mosses, very diverse in modern ecosystems, are currently underrepresented in the fossil record. For the pre-Cenozoic, fossil mosses are known almost exclusively from compression fossils, while anatomical preservation, which is much more taxonomically informative, is rare. The Lower Cretaceous of Vancouver Island (British Columbia, Canada) hosts a diverse anatomically preserved flora at Apple Bay. While the vascular plant component of the Apple Bay flora has received much attention, the numerous bryophytes identified at the locality have yet to be characterized. METHODS: Fossil moss gametophytes in more than 20 carbonate concretions collected from the Apple Bay locality on Vancouver Island were studied in serial sections prepared using the cellulose acetate peel technique. KEY RESULTS: We describe Tricosta plicata gen. et sp. nov., a pleurocarpous moss with much-branched gametophytes, tricostate plicate leaves, rhizoid-bearing bases, and delicate gametangia (antheridia and archegonia) borne on specialized branches. A new family of hypnanaean mosses, Tricostaceae fam. nov., is recognized based on the novel combination of characters of T. plicata. CONCLUSIONS: Tricosta plicata reveals pleurocarpous moss diversity unaccounted for in extant floras. This new moss adds the first bryophyte component to an already diverse assemblage of vascular plants described from the Early Cretaceous at Apple Bay and, as the oldest representative of the Hypnanae, provides a hard minimum age for the group (136 Ma). [ABSTRACT FROM AUTHOR]

* Premise of the study: Triassic and Jurassic fossils record structural changes in conifer seed cones through time, provide the earliest evidence for crown-group conifer clades, and further clarify sister-group relationships of modern conifer families. A new and distinct seed-cone from the Isle of Skye in western Scotland provides the oldest detailed evidence for the ancestral morphology of the phylogenetically contentious family Cupressaceae. * Methods: A single isolated cone was prepared as serial sections by the cellulose acetate peel technique, mounted on microscope slides, and viewed and photographed using transmitted light. The three-dimensional structure of the cone was first reconstructed from the serial sections and then refined through imaging with x-ray microtomography. * Key results: Scitistrobus duncaanensis, gen. et sp. nov., is a 7.5 mm-diameter cylindrical seed cone with helically arranged bract-scale complexes in which three scale tips separate from a large bract, each tip bearing one adaxial seed. Seeds are nearinverted, show 180° rotational symmetry, and have a diminutive wing in the major plane. * Conclusions: Scitistrobus duncaanensis extends the fossil record for anatomically preserved seed cones of the Cupressaceae backward from the Upper Jurassic to the Aalenian Stage of the Middle Jurassic. The cone displays a previously unknown combination of characters that we regard as diagnostic for seed cones of early-divergent Cupressaceae and helps to clarify the sequence of structural changes that occurred during the transition from ancestral voltzialean conifers to morphologically recognizable Cupressaceae. Hypotheses of homology underpinning such transformational series can be tested by ongoing reciprocal illumination between the morphology of fossil taxa and the morphogenesis and developmental genetics of their extant crown-group relatives. [ABSTRACT FROM AUTHOR]

Premise of the study: Two ovulate conifer cones, one of which is attached terminally to a short leafy shoot, reveal the presence of a new species of Hughmillerites in the Early Cretaceous Apple Bay flora of Vancouver Island, British Columbia, Canada. This ancient conifer expands the diversity of Cupressaceae in the Mesozoic and reveals details about the evolution of Subfamily: Cunninghamioideae. • Methods: Specimens were studied from anatomical sections prepared using the cellulose acetate peel technique. • Key results: Vegetative shoots have helically arranged leaves that are CunninghamiaAike. Seed cones have many helically arranged bract/scale complexes in which the bract is larger than the ovuliferous scale. Each ovuliferous scale has three free tips that separate from the bract immediately distal to an inverted seed. Several ovuliferous scales show interseminal ridges between seeds. • Conclusions: This study documents a new extinct species of cunninghamioid conifers, Hughmillerites vancouverensis, expanding the record of the genus from the Late Jurassic to the Early Cretaceous. This new extinct species emphasizes the important role that conifers from subfamily Cunninghamioideae played in the initial evolutionary radiation of Cupressaceae. In light of recent findings in conifer regulatory genetics, we use H. vancouverensis to hypothesize that variations of expression in certain gene homologues played an important role in the evolution of the cupressaceous ovuliferous scale. [ABSTRACT FROM AUTHOR]

Early Cretaceous fossilized leaves assignable to the extinct seed plant order Bennettitales occur within an exceptionally diverse Early Cretaceous (Valanginian) flora of anatomically preserved plant fossils at Apple Bay on Vancouver Island, British Columbia, Canada. One of the bennettitalean leaf types has an entire margin, with laminae that are attached near the adaxial surface of the midvein. Leaves are 10-15 mm wide with an adaxial surface that shows distinct corrugations, and a midrib that is exposed adaxially. The vascular system of the midrib consists of a crescent-shaped ring of collateral bundles. Lateral veins diverge from midrib at ∼90°, are typically simple but occasionally branch at base of the lamina. Vein density is 12-15 per cm. Leaves are hypostomatic with syndetocheilic stomata that are randomly oriented between veins. Internal anatomy consists of an adaxial hypodermis of closely-spaced isodiametric cells, mesophyll that is differentiated into adaxial palisade and abaxial spongy zones, and collateral bundles that show a distinct bundle sheath with bundle sheath extensions. This novel combination of characters represents the diverse bennettitalean genus Nilssoniopteris. Nilssoniopteris corrugata new species is only the second species of the genus for which internal anatomy is preserved. This species increases the known variation of bennettitalean leaf anatomy, and reinforces our appreciation for the global distribution of bennettitalean seed plants during the Mesozoic. [ABSTRACT FROM AUTHOR]

A fossil seed cone with characters that have been hypothesized as transitional to the origin of crown group gnetophytes has been discovered in Lower Cretaceous deposits on Vancouver Island, British Columbia, Canada. This cone, described as Protoephedrites eamesii gen. et sp. nov., provides the first anatomically preserved fossil evidence for the evolution of gnetophyte cones with seeds. The cone is a compound shoot system consisting of a primary axis with nodes that bear bracts and axillary fertile shoots in an opposite/decussate arrangement. The secondary fertile shoot axis produces one or two pairs of diminutive bracteoles and a pair of erect ovules in an opposite/decussate pattern. In contrast to crown group gnetophytes, bracteoles subtend rather than surround and enclose the ovules. Ovules have a single multiseriate integument that is adnate to the nucellus in the basal region and free distally. The micropylar tube is short with a thick integument, but it displays distinctive cells of the inner integumentary epidermis that are characteristic of gnetophyte seeds. Each seed produces a large pollen chamber with a uniseriate wall. Paired erect ovules conform to the pleisomorphic morphology previously hypothesized for Ephedra seed cones, thus supporting the proposal that ancestral gnetophyte seeds are borne terminally on oppositely arranged sporophylls. The combination of gnetophyte synapomorphies and putative pleisomorphic characters displayed by Protoephedrites broadens the known range of morphologies for the most ancient gnetophytes. Detailed comparisons to several species of Bennettitales confirm that there are fundamental structural differences separating the seeds of Gnetales from those of Bennettitales, support the hypothesis that the outer seed envelope evolved within the gnetophyte clade, and suggest that Bennettitales are not as closely related to Gnetales as hypothesized by some authors. [ABSTRACT FROM AUTHOR]

Evolution of plant form proceeds through sequential alterations in the development of plant organs. Leaves (or fronds) are organs that have diagnostic characteristics, including definite arrangement on a stem, bilateral symmetry (abaxial/adaxial identity), and determinate growth. Evolution of those diagnostic characteristics represents a series of critical steps in plant evolution that resulted from specific developmental alterations. The fossil record reveals a transformational series in leaf evolution that highlights steps that have occurred in parallel but independently in both leptosporangiate ferns and seed plants, resulting in superficially similar frond morphologies. In this study, the fronds of the most ancient fossil fern, Psalixochlaena antiqua, and the most ancient reconstructed seed plant, Elkinsia polymorpha, are characterized and compared with leaves of modern plants in order to identify the sequence in which features of leaves in two distinct clades of euphyllophytes arose. While both fronds show a combination of characters attributable to ancestral vegetative axes and characters attributable to leaves, each plant displays different combinations of those characters. These data document dissimilar sequences of character originations and, therefore, the independent evolution of developmental mechanisms in seed plants and ferns. [ABSTRACT FROM AUTHOR]

Recent phylogenetic analyses have yielded conflicting results regarding relationships among ferns and other major groups of vascular plants and have prompted some authors to propose novel patterns of tracheophyte phylogeny based on analyses that include only living taxa. The results of one such study resolve seed plants as the sister group to all nonlycophyte pteridophytes and place equisetophytes and psilotophytes within a clade that also includes all of the living ferns. That hypothesis of phylogeny differs markedly from the results of a recent analysis that utilizes morphological data from both living and extinct taxa, which resolves ferns as a polyphyletic assemblage. To evaluate these competing hypotheses and to increase our understanding of the differing results, several tests were performed. Tests identify a high level of character conflict among the various gene sequence data matrices used in the analysis of living taxa. Contrary to the expectations of some, inclusion of extinct taxa in analyses of morphological characters produces striking changes in the topology of the resulting vascular plant tree when compared with the analysis of living taxa only. Together, these tests reveal that relationships among major groups of vascular plants are far less completely understood than claimed by some and that ferns s.l. are probably a polyphyletic assemblage. They also suggest that the impressive successes of gene sequence data in resolving relationships within smaller clades may not be easily duplicated when addressing deep internal nodes of the polysporangiophyte tree. Additional refinement of morphological characters for a combination of living and well-reconstructed extinct taxa, improved character/taxon ratios, fuller sampling of extinct clades, and tests that utilize rare genetic markers and developmental pathways may hold the greatest promise for ultimately resolving the overall pattern of vascular plant phylogeny. [ABSTRACT FROM AUTHOR]

Trawetsia princetonensis Smith, Stockey, Nishida & Rothwell gen. et sp. nov. is described from several permineralized rhizomes, stipes, and higher-order frond members of a blechnoid fern that have been identified from the Middle Eocene Princeton Chert of British Columbia. Rhizomes bear stipes arising from all sides of the stem as well as diarch adventitious roots. The dictyostelic rhizomes are up to 16 mm across and have five to seven amphiphloic cauline bundles that are capped internally and externally by sclerenchyma. Ground tissue, where well preserved, is transitional from arenchymatous toparenchymatous, with abundant small sclerotic nests found throughout the pith and cortex. Multicellular scales are borne on the rhizome but are sparse and do not imbricate. At least three orders of frond material are preserved: stipes, primary pinnae, and laminar pinnules. Stipes have an adaxial groove, two adaxial hippocampiform bundles, and seven or fewer small, circular bundles arranged in an abaxial U-shaped arc. In distal sections of the rachis, the vascular bundles are reduced to three or fewer. Ground tissue of the stipe has sclerenchyma nests near the base but distally becomes completely aerenchymatous, further evidence that the Princeton Chert preserves an ancient wetland environment. This fossil material expands our knowledge of fern diversity from the Princeton Chert locality, which also includes osmundaceous, dennstaedtioid, and dryopterid ferns, and it contributes to the understanding of the timing and evolution of derived Filicales. While the vegetative anatomy of this fern allies it with the Blechnaceae, the lack of attached fertile fronds precludes the possible recognition of T. princetonensis as a fossil representative of a modern genus or perhaps even a living species. [ABSTRACT FROM AUTHOR]

A new fossilized walchian (Voltziales) conifer plant from the Late Pennsylvanian Hamilton Quarry of Kansas, U.S.A. combines morphological characters of the morphogenus Waichia and the fossil plant genus Otovicia, with cuticular characters like those of the fossil plant genus Ernestiodendron, and seed cone morphology like that of the fossil plant genus Emporia. Internal anatomical characters are basically similar to the other walchian genera for which such features are known, but some are taxonomically informative. Numerical cladistic analysis reveals that this novel combination of characters defines a new fossil plant genus and species of walchian conifers Hanskerpia hamiltonensis. This analysis provides a test of hypotheses for relationships among walchian and other ancient conifers. Results of this analysis support some previously proposed relationships among the most primitive conifers and other Paleozoic coniferophytes. However, the analysis also calls to question the validity of all previously proposed familial circumscriptions for walchian conifers, and highlights the perplexing systematic challenges posed by the most ancient fossil conifers. The unexpected species richness of voltzialean conifers is interpreted as having resulted from the evolutionary ecology of unstable environments. [ABSTRACT FROM AUTHOR]

Permineralized cyatheaceous sori occur among remains of conifers, fungi, and other plants in newly discovered calcareous concretions from Early Cretaceous (Barremian) marine sediments of Vancouver Island, British Columbia, Canada. Sori are superficially attached in two rows to narrow pinnules and display a globose sphaeropteroid indusium. Annulate sporangia with multicellular stalks diverge from a basal, vascularized receptacle. The nearly vertical uniseriate annulus is not interrupted by the stalk. The sporangia bear 64 trilete spores with perispore sculpturing that ranges from irregular granulate/echinate to prominent rodlets. These specimens, described as Cyathea cranhamii sp. nov., are the first anatomically preserved tree fern sori from the fossil record. They represent the most ancient evidence for fertile structures of the Cyatheaceae and demonstrate that essentially modern species of cyatheaceous tree ferns had evolved by the Early Cretaceous. [ABSTRACT FROM AUTHOR]

In this paper we report the first occurrence of permineralized plant fossils in volcaniclastic lithologies from China and in doing so describe a new species of cardiocarpalean ovule permineralized within tuffaceous sediments from a recently discovered locality near Pingquan, Hebei Province, North China. The tuff is part of the Early Permian Taiyuan Formation which contains a diverse fossil plant assemblage that includes cordaitean spermatophytes, lepidodendralean lycophytes, equisetophytes, and filicalean ferns, all of which were typical of Permian floras of northern China at this time. Specimens of Cardiocarpusdabiziae sp. nov. have the characteristic platyspermic shape and vascularization of cardiocarpalean ovules, and display prominent protuberances on the exterior of the integument. The integument of the ovule is composed of three layers; a thick sarcotesta, a thin and comparatively dense sclerotesta, and a single layer of large endotesta cells. The pollen chamber produces a slender nucellar beak. In several specimens the megaspore membrane contains well-developed tissue of the megagametophyte. The ovules have prominent external integumentary protuberances which suggest that well-developed systems of plant/animal interactions were operative in Early Permian wetland biotas of the Cathaysian realm. [ABSTRACT FROM AUTHOR]

Fossil woods are preserved as calcareous permineralizations in the Upper Cretaceous Northumberland Formation on Collishaw Point, Hornby Island, British Columbia, Canada. They are well preserved, often including peripheral tissues, and reveal the diversity and structure of vegetation in the region ca. 72 million years ago. We describe a new genus and species based on two specimens. Two specimens were cut using a rock saw to expose the fossil wood in transverse and longitudinal sections. Thin sections were prepared using the cellulose acetate peel technique. Peels were mounted on slides with Eukitt mounting medium. Anatomical description follows the IAWA guidelines. We compared the anatomy of the fossils with that of other plants using data available in the published literature and the InsideWood database. The combination of wide vessels and high vessel frequency given the narrow diameter of the stem, combined with the abrupt increase in vessel diameter near the pith indicates this plant had hydraulic properties typical of a climbing plant (liana). The anatomy of the rays, the arrangement of the vessels and their pitting, and the thickness of the bark are also consistent with the climbing habit, but not diagnostic of any extant family. This is the second species of liana to be described from the Hornby Island assemblage, providing new information about the composition of structurally complex mixed conifer–angiosperm forests in the Late Cretaceous of western North America. [ABSTRACT FROM AUTHOR]

Evaluates the features of Osmunda cinnamomea from the Upper Cretaceous Horseshoe Canyon Formation in southern Alberta and other permineralized O. cinnamomea-like fossils. Fossils' conformity to the living species; Hypothesis that species longevity in homosporous pteridophytes may be far greater than commonly recognized; Example of a fossil filicalean fern.

Focuses on the resolution of the relationships of the Lemnaceae using morphological characters of fossils and extant species. Interconnection of rosettes by stolons; Characterization of the leaves; Description of the pollen wall; Advantages of the completeness of Limnobiophyllum scutatum.

Reports on fossil ectomycorrhizae from the British Columbia. Effects of hormones produced by living ectomycorrhizal fungi; Evolution of mycorrhizal associations; Features of the Princeton chert fossils; Characterizations of the mycorrhizal rootlets.

Abstract: This paper provides a whole plant concept for a new species, Emporia cryptica sp. nov. Hernandez-Castillo, Stockey, Rothwell & Mapes (Emporiaceae: Voltziales), the fourth conifer to be reconstructed from the rich fossil biota at the Late Pennsylvanian, Hamilton Quarry, Kansas. E. cryptica has an orthotropic stem, lateral plagiotropic branches with simple leaves, simple pollen cones, and compound ovulate cones. Branches have an endarch eustele with dense wood surrounding a parenchymatous pith with sclerotic nests/plates, and secondary xylem tracheids with multiseriate hexagonal bordered pits. Leaves on both penultimate and ultimate branches are simple and amphistomatic with two adaxial stomatal bands, monocyclic and dicyclic stomata, and two narrow abaxial rows of stomata with numerous trichome bases. Pollen cones are simple with helically arranged microsporophylls and adaxial pollen sacs. Prepollen is monolete, eusaccate, and monosaccate (Potonieisporites Bharadwaj). Ovulate cones are compound with bilaterally symmetrical dwarf shoots in the axils of helically arranged forked bracts. Axillary dwarf shoots bear numerous sterile scales interspersed with two megasporophylls, each bearing a single inverted terminal ovule. This plant displays morphological and cuticular characters similar to several morphogenera of Paleozoic walchian conifers but is most comparable to the fossil plant species Emporia lockardii and Hanskerpia hamiltonensis. E. cryptica is the only walchian conifer where ovules and seeds with megagametophytes, immature embryos and mature embryos have been documented, demonstrating that the most ancient conifers possessed seed dormancy and polycotyledonary embryos. This reproductive biology is similar to that of many Mesozoic and extant conifers with saccate pollen except for the presence of prepollen grains that are common among Paleozoic walchian conifers. [Copyright &y& Elsevier]