Gar Rothwell
Ohio University, Environmental and Plant Biology, Faculty Member
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... Printed in The Netherlands A REINTERPRETATION OF THE PALEOZOIC FERN NORWOODIA ANGUSTUM CHARLES W. GOOD and GAR W. ROTHWELL ... have been as-signed to the Coenopteridales on the basis of vegetative features (eg, Morgan and Delevor-yas,... more
... Printed in The Netherlands A REINTERPRETATION OF THE PALEOZOIC FERN NORWOODIA ANGUSTUM CHARLES W. GOOD and GAR W. ROTHWELL ... have been as-signed to the Coenopteridales on the basis of vegetative features (eg, Morgan and Delevor-yas, 1954). ...
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... 1965), features used in the elucidation of taxonomic problems (Hoskins and Cross, 1946; Taylor, 1965), ovule ontogeny (Rothwell, 1971, 1980 ... pollen chamber of Stephanospermum costatum is conspicuous (Plate I, 1). Histologically, it... more
... 1965), features used in the elucidation of taxonomic problems (Hoskins and Cross, 1946; Taylor, 1965), ovule ontogeny (Rothwell, 1971, 1980 ... pollen chamber of Stephanospermum costatum is conspicuous (Plate I, 1). Histologically, it possesses a prominent outer wall that often ...
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Numerous anatomically preserved fragments of the Middle Pennsylvanian age filicalean fern, Botryopteris tridentata, occur in coal balls collected at the Pittsburgh and Midway Coal Company mine near Baxter Springs, Kansas. Included are the... more
Numerous anatomically preserved fragments of the Middle Pennsylvanian age filicalean fern, Botryopteris tridentata, occur in coal balls collected at the Pittsburgh and Midway Coal Company mine near Baxter Springs, Kansas. Included are the first fertile specimens of the species, evidence of complete vegetative frond architecture, and fronds that are specialized for vegetative propagation. Rhizomes are erect and unbranched, have helical phyllotaxis and short internodes, and typically display an ectophloic solenostele. Fronds are tripinnately compound with lobed pinnules that have open, dichotomous venation. Fertile pinnae or individual pinnules are interspersed among vegetative frond segments and produce sori of annulate sporangia beneath veins on the abaxial pinnule surface. Fertile pinnule lobes are rolled toward the abaxial surface to enclose the sori. Sporangia have a horizontally elongated biseriate annulus located near the short broad stalk and produce tetrahedral-shaped trilete spores with coarse spines. Epiphyllous branches diverge from the stipe or rachis, and some fronds produce only branches. This fern is reconstructed as having short stems. Helically arranged fronds are either pinnately dissected with lobed vegetative pinnules and abaxially rolled fertile pinnules or are specialized for vegetative propagation. The latter functioned as the foliar equivalent of stolons. While some characters of the B. tridentata plant are similar to those of Botryopteris forensis, generitype of the Botryopteridaceae, others are more comparable to those of Psalixochlaena cylindrica, generitype of Psalixochlaenaceae, suggesting the need for reevaluation of systematic relationships among species of the Botryopteridaceae and Psalixochlaenaceae.
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The monostelic seed fern Schopfiastrum decussatum Andrews is described from a specimen collected at a Middle Pennsylvanian petrifaction locality in southern Illinois. The specimen measures 24 cm long and is about 1.1 cm in diameter. Two... more
The monostelic seed fern Schopfiastrum decussatum Andrews is described from a specimen collected at a Middle Pennsylvanian petrifaction locality in southern Illinois. The specimen measures 24 cm long and is about 1.1 cm in diameter. Two petioles are attached to the axis and abundant foliar material is also present. Leaf arrangement is alternate and distichous. The stem consists of an exarch protostele surrounded by a prominent zone of secondary xylem. Secondary phloem and a vascular cambium are also preserved. The cortex is characterized by an undulating outer epidermal zone consisting of alternating ridges and furrows; internally this zone is delimited by conspicuous lacunae. Sclerenchyma bands occur in the outer cortex, with prominent resin canals present in the inner cortex. The fronds are represented by dichotomizing rachides, primary pinnae, and laminar pinnules. Features of the plant are compared to those of other Carboniferous pteridosperms, and a reconstruction of Schopfiastrum is included.
Research Interests: Botany, Geology, Paleontology, Plant Biology, Biology, and 7 moreAnatomy, Carboniferous, Xylem, Phloem, Pennsylvanian, Cambium, and Stele
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... Line indicates level at which stalk in 4 was sectioned. 422D bot (c), 20 x 70. (a = appendage, ca = cone axis, w = sporangial wall.) Page 5. 1198 SUSAN D. RIGGS AND GAR W. ROTHWELL IT. 4 1 - 1 ? .. r .-,VjZ . . - t - 'I... more
... Line indicates level at which stalk in 4 was sectioned. 422D bot (c), 20 x 70. (a = appendage, ca = cone axis, w = sporangial wall.) Page 5. 1198 SUSAN D. RIGGS AND GAR W. ROTHWELL IT. 4 1 - 1 ? .. r .-,VjZ . . - t - 'I " 0 ;.. rr .. . ,. _.-... 4 , t - ' " IZ IV Vw Irv. ? 't 4? F4 ..0 ...
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... 1, fig. 1) clearly demonstrates that the ovules described by Rothwell (1971) are not C. oblongum. ... cupule or at the tip of a stalk. Conostoma ob-longum may have been borne on the inner obliquewall of a cupulate branching system... more
... 1, fig. 1) clearly demonstrates that the ovules described by Rothwell (1971) are not C. oblongum. ... cupule or at the tip of a stalk. Conostoma ob-longum may have been borne on the inner obliquewall of a cupulate branching system such as in Eurystoma angulare (Long, 1960). ...
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A large collection of anatomically preserved marattialean stem and trunk segments from the Upper Pennsylvanian of Ohio provides the basis for detailed structural and taxonomic studies of several Psaronius species. Nineteen of the... more
A large collection of anatomically preserved marattialean stem and trunk segments from the Upper Pennsylvanian of Ohio provides the basis for detailed structural and taxonomic studies of several Psaronius species. Nineteen of the specimens form an intergrading ...
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Research Interests: Botany, Plant Biology, Biology, Anatomy, Permian, and 4 morePaleozoic, Pennsylvanian, Sclerotium, and medulla
A rich fossil biota from a Pennsylvanian age deposit of eastern North America contains numerous vegetative and fertile specimens that conform to a single species of primitive walchian conifers. Among the specimens is a compound pollen... more
A rich fossil biota from a Pennsylvanian age deposit of eastern North America contains numerous vegetative and fertile specimens that conform to a single species of primitive walchian conifers. Among the specimens is a compound pollen cone that comprises closely spaced, helically arranged, leaf‐like bracts with axillary dwarf shoots. The specimen looks superficially similar to an ultimate vegetative conifer shoot, but there are small appendages in the axil of each bract that represent the fertile dwarf shoots. Dwarf shoots consist of an axis that bears sterile scales and sporophylls with erect pollen sacs. Pollen found in the sacs is monosaccate and conforms to the sporae dispersae genus Potonieisporites Bhardwaj. This cone is a compound shoot system that is morphologically equivalent to the ovulate cones of conifers and to the pollen cones of Paleozoic cordaitaleans and modern gnetophytes. Therefore, it is fundamentally different from the simple pollen cones of other fossil and modern conifers. Discovery of this specimen unexpectedly supports molecular studies that predict a close relationship between Coniferales and Gnetales, and provides fossil evidence to help reconcile the discordant phylogenetic hypotheses of seed plant systematics that have been developed from morphological and molecular data.
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Research Interests: Geology and Pennsylvanian
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Numerous specimens of the pteridospermous pollen organs Idanothekion glandulosum and Callandrium callistophytoides are present in Middle and Upper Pennsylvanian petrifaction material, respectively. Several specimens of Idanothekion,... more
Numerous specimens of the pteridospermous pollen organs Idanothekion glandulosum and Callandrium callistophytoides are present in Middle and Upper Pennsylvanian petrifaction material, respectively. Several specimens of Idanothekion, previously known only in an isolated condition, are attached to foliage assignable to the monostelic seed fern Callistophyton. Proof of the affinities of Idanothekion allows this genus to be elevated from a form genus to an organ genus in the Callistophytaceae. The structure of the foliage and the mode of attachment of the Idanothekion specimens are like those previously described for Callandrium. Structural features of Idanothekion and Callandrium are compared, and the question of their identity is discussed. At present one basic type of pollen organ, borne on the abaxial surface of foliar pinnules, is known for members of the Callistophytaceae.
Research Interests: Botany, Evolutionary Biology, Plant Biology, Biology, Ecology, and 4 morePollen, fERN, Genus, and Pennsylvanian
... but ob-scure in cross sections of cordaitean stems (ROTH-WELL 1977; TRIVETr and ROTHWELL 1 985) . In longitudinal sections at the pith-xylary bound-ary of M. priapi (figs. 15-17), the innermo,st tra-cheids between the leaf traces have... more
... but ob-scure in cross sections of cordaitean stems (ROTH-WELL 1977; TRIVETr and ROTHWELL 1 985) . In longitudinal sections at the pith-xylary bound-ary of M. priapi (figs. 15-17), the innermo,st tra-cheids between the leaf traces have scalariform wall-thickening patterns ...
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Research Interests: Biology and Sporangium
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Among the unique and intriguing features that make ginkgophytes some of the most fascinating of seed plants is the rich fossil record for a clade that is monotypic in the modern flora, and for which there may be no natural populations in... more
Among the unique and intriguing features that make ginkgophytes some of the most fascinating of seed plants is the rich fossil record for a clade that is monotypic in the modern flora, and for which there may be no natural populations in the wild [1]. Numerous apparently primitive features contribute to the systematic intrigue of ginkgophytes and to their apparently crucial role in seed plant evolution. Meyen [2] considered Ginkgo to represent one of three major groups of seed plants, Florin [3] interpreted Ginkgo to have evolved in parallel to conifers. Emberger [4] interpreted Ginkgo to be little changed in its reproductive biology from the most ancient seed plants, and modern cladistic analyses place Ginkgo below all or nearly all other living species on the seed-plant tree [e.g., 5–7].
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The discovery of pedunculate specimens of pollen organ Dolerotheca in close association with Myeloxylon-type pinnae and Alethopteris-type pinnules provides evidence for the reconstruction of a petrified medullosan frond and the attachment... more
The discovery of pedunculate specimens of pollen organ Dolerotheca in close association with Myeloxylon-type pinnae and Alethopteris-type pinnules provides evidence for the reconstruction of a petrified medullosan frond and the attachment of the microsporangiate fructification. Specimens of Dolerotheca villosa and D. formosa from Middle and Upper Pennsylvanian age strata of North America are borne on slender peduncles with anatomical features and vascularization identical to those of some level in a Myeloxylon-Alethopteristype frond. Reconstruction of the frond reveals a large, repeatedly dichotomising organ that bears penultimate pinnae and ultimate pinnules in a pinnate arrangement. Examination of pinnules on the surface of coal ball material indicates that they conform to the compression genus A lethopteris. Identical numbers and arrangement of vascular bundles together with identical anatomical features and multicellular hairs indicate that the Dolerotheca campanulum is borne in the position of a penultimate pinna. A reconstruction of the frond with a proposed polled organ attachment is included.
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This paper explores the potential role of developmental changes in the macroevolution of vascular plants. The discussion is focused on an explanation of the concept of heterochrony, on factors that render it compatible with and/or... more
This paper explores the potential role of developmental changes in the macroevolution of vascular plants. The discussion is focused on an explanation of the concept of heterochrony, on factors that render it compatible with and/or supplementary to classical neo-Darwinian ...
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The discovery of well preserved, permineralized plant remains in Eocene sediments near Princeton, British Columbia, provides an opportunity to describe Metasequoia milleri, a new species of taxodiaceous pollen cone. Individual specimens... more
The discovery of well preserved, permineralized plant remains in Eocene sediments near Princeton, British Columbia, provides an opportunity to describe Metasequoia milleri, a new species of taxodiaceous pollen cone. Individual specimens are up to 3.0 mm long and 2.9 mm in diameter and are subtended by a vegetative zone of scale-like leaves. Approximately 30 microsporophylls are attached to the axis, and each bears three ovoid pollen sacs. The distal-most subtending leaves imbricate and enclose the fertile region. Pollen is ovoid to subspheroidal with an erect, protruding leptoma. Grains measure 19–27 μn in diameter and have verrucate exine ornamentation with numerous orbicules. These fossils show that pollen cones anatomically similar to those of extant Metasequoia glyptostroboides were present as early as Middle Eocene time.
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A noncellular substance containing pollen and spores has been discovered protruding from the micropyle of a seed fern ovule of Middle Pennsylvanian age. This provides direct evidence that pollination-drop mechanisms comparable to those of... more
A noncellular substance containing pollen and spores has been discovered protruding from the micropyle of a seed fern ovule of Middle Pennsylvanian age. This provides direct evidence that pollination-drop mechanisms comparable to those of many extant gymnosperms characterize some Paleozoic pteridosperms.
Research Interests: Science, Biology, Pollination, Medicine, Multidisciplinary, and 5 morePollen, Paleozoic, Pennsylvanian, Spore, and ovule
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Well preserved, permineralized plant material from the Middle Eocene, Allenby Formation of British Columbia provides the basis for this description of an extensive Tertiary flora. The flora comprises a diverse assemblage of abundant plant... more
Well preserved, permineralized plant material from the Middle Eocene, Allenby Formation of British Columbia provides the basis for this description of an extensive Tertiary flora. The flora comprises a diverse assemblage of abundant plant remains in a chert matrix which outcrops south of Princeton, B.C., Canada. Preliminary examination of this material reveals numerous fertile and vegetative organs of angiosperms, conifers, ferns, bryophytes, and fungi, most of which represent presently unknown taxa. Initial studies indicate that we are dealing with the most diverse Eocene permineralization flora ever discovered. Superb anatomical preservation, including developmental stages of various organs, characterize many of the taxa and promise to significantly increase our knowledge of early Tertiary plants.
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Numerous compression – limonitized specimens of small, delicate branch systems have been discovered in the Upper Devonian Hampshire Formation near Elkins, West Virginia. The fossils are described as Gillespiea randolphensis gen. et... more
Numerous compression – limonitized specimens of small, delicate branch systems have been discovered in the Upper Devonian Hampshire Formation near Elkins, West Virginia. The fossils are described as Gillespiea randolphensis gen. et sp.nov., and assigned to the Stauropteridales. Axes are smooth and slender, range from less than 0.1 to 1.1 mm wide, and display quadriseriate branching. The largest axes of each system bear alternating pairs of smaller lateral axes, and this pattern is repeated in all but the smallest orders of branching. All axes are protostelic, consisting of a solid xylem core with marginally mesarch protoxylem strands, a narrow zone of putative phloem, and cortex. In transverse sections, steles of larger axes are three-to four-angled and have one to three protoxylem strands at each angle. Steles of the smaller axes are elliptical or round in cross section. Small, bifurcating lateral axes that bear sporangia are attached at the levels of branching and terminate the larger systems. Megasporangia are approximately 0.6 mm long and 0.3 mm wide, and contain one or two radial, trilete megaspores. Microsporangia have not been identified. This species extends the stratigraphic range of the Stauropteridales from the Carboniferous back to the Upper Devonian and demonstrates that the group had attained the grade of extreme heterospory by the Famennian.
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... Scanning electron micrographs of broken wall surfaces and internal views of the wall reveal that the exine is composed of a ... LYCOPSIDA) FROM THE UPPER PENNSYLVANIAN OF THE APPALACHIAN BASIN BING-CHENG FENG and GAR W. ROTHWELL... more
... Scanning electron micrographs of broken wall surfaces and internal views of the wall reveal that the exine is composed of a ... LYCOPSIDA) FROM THE UPPER PENNSYLVANIAN OF THE APPALACHIAN BASIN BING-CHENG FENG and GAR W. ROTHWELL Department of ...
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... et Rothwell. Emended specific diagnosis. Prostrate rhizome up to 1.33.0 mm in diameter with attached stipe bases. Dictyostele composed of four to five oval meristeles 0.41.2 mm long and 0.20.4 mm thick. Metaxylem 28 97 μm in... more
... et Rothwell. Emended specific diagnosis. Prostrate rhizome up to 1.33.0 mm in diameter with attached stipe bases. Dictyostele composed of four to five oval meristeles 0.41.2 mm long and 0.20.4 mm thick. Metaxylem 28 97 μm in diameter with scalariform wall‐thickening ...
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Research Interests: Botany, Evolutionary Biology, Plant Biology, Biology, Xylem, and 3 morePlant sciences, fERN, and Phyllotaxis
New ovules from the Fayetteville Formation (Upper Mississippian) of Arkansas expand our knowledge of the morphology and anatomy of Rhynchosperma and suggest it was produced by a medullosan seed fern. Rhynchosperma has been described as... more
New ovules from the Fayetteville Formation (Upper Mississippian) of Arkansas expand our knowledge of the morphology and anatomy of Rhynchosperma and suggest it was produced by a medullosan seed fern. Rhynchosperma has been described as radially symmetrical with a two-layered integument and vascularization in the integument only. The apical portion of the integument is ribbed; the nucellus is fused to the integument and apically differentiated into a dome-shaped pollen chamber. The vascular system is incompletely known and apparently restricted to the base of the integument. The new specimens are like Rhynchosperma in external shape, size, number of ribs, and numerous histological features. However, new data reveal that the nucellus is vascularized by a sheath of tracheids, the integument is vascularized by discrete bundles, the pollen chamber has a nucellar beak, and the nucellus is attached to the integument for a variable distance from the base. In addition, the integument is tripartite with an elaborate apical region; ribs formed by the integument are more pronounced at the apex; and internally open, hollow lobes form a stellate micropylar canal. The presence of a tripartite integument, the nature of the vascular system, the nucellus-integument attachment, the pollen chamber structure, symmetry, and the association with medullosan vegetative remains suggest medullosan affinity for these ovules and strengthens the evidence for the origin of the family before the end of the Lower Carboniferous.