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Activating mutations in the neuroblastoma rat sarcoma viral oncogene homolog (NRAS) gene are common genetic events in malignant melanoma being found in 15–25% of cases. NRAS is thought to activate both mitogen activated protein kinase (MAPK) and PI3K signaling in melanoma cells. We studied the influence of different components on the MAP/extracellular signal-regulated (ERK) kinase (MEK) and PI3K/mammalian target of rapamycin (mTOR)-signaling cascade in NRAS mutant melanoma cells. In general, these cells were more sensitive to MEK inhibition compared with inhibition in the PI3K/mTOR cascade. Combined targeting of MEK and PI3K was superior to MEK and mTOR 1,2 inhibition in all NRAS mutant melanoma cell lines tested, suggesting that PI3K signaling is more important for cell survival in NRAS mutant melanoma when MEK is inhibited. However, targeting of PI3K/mTOR 1,2 in combination with MEK inhibitors is necessary to effectively abolish growth of NRAS mutant melanoma cells in vitro and regress xenografted NRAS mutant melanoma. Furthermore, we showed that MEK and PI3K/mTOR 1,2 inhibition is synergistic. Expression analysis confirms that combined MEK and PI3K/mTOR 1,2 inhibition predominantly influences genes in the rat sarcoma (RAS) pathway and growth factor receptor pathways, which signal through MEK/ERK and PI3K/mTOR, respectively. Our results suggest that combined targeting of the MEK/ERK and PI3K/mTOR pathways has antitumor activity and might serve as a therapeutic option in the treatment of NRAS mutant melanoma, for which there are currently no effective therapies.

Interregional correlation of the marine zones of major cyclothems between North America and eastern Europe does not support assertions that a major stratigraphic gap exists between the traditional regional Desmoinesian and Missourian stages in North America. Such a gap was previously proposed to explain an abrupt change in megafloral assemblages in the northern Appalachian Basin and by extension across all of North America. Conodont-based correlation from the essentially complete low-shelf Midcontinent succession (distal from the highstand shoreline), through the mid-shelf Illinois Basin, to the high shelf of the Appalachian Basin (proximal to highstand shoreline) demonstrates that all major ,400 kyr cyclothem groupings in the Midcontinent are recognizable in the Illinois Basin. In the Appalachian Basin, however, the grouping at the base of the Missourian is represented only by paleosols and localized coal. The immediately preceding grouping was removed very locally by paleovalley incision, as is evident at the 7–11 Mine, Columbiana County, Ohio, from which the original megafloral data were derived. At the few localities where incised paleodrainage exists, there may be a gap of ,1000 kyr, but a gap of no more than ,600 kyr occurs elsewhere in the Appalachian Basin at that level and its magnitude progressively decreases westward into the Illinois (,300 kyr) and Midcontinent (,200 kyr) Basins. Thus, while a gap is present near the Desmoinesian–Missourian boundary in North America, it is typically more than an order of magnitude smaller than that originally proposed and is similar to the gaps inferred at sequence boundaries between cyclothems at many horizons in the Pennsylvanian of North America.

The Tedeleaceae are late Paleozoic Filicalean ferns with two known genera, Ankyropteris and Senftenbergia, which partially overlap morphologically and have the same known stratigraphic ranges—Namurian A to Lower Permian in Euramerica. Ankyropteris is anatomically known and Senftenbergia is almost exclusively based on compression specimens. Both genera exhibit abaxially, laminar-borne sori and/or solitary sporangia with some schizaeoid attributes. The sporangia are pyriform to tear-drop shaped, erect to slightly curved with a two to multiseriate apical annulus and mature spores usually of the Raistrickia type. Detailed morphological comparisons of Ankyropteris with Senftenbergia emphasize generic overlaps as well as lack of congruence. Ankyropteris brongniartii, a classic vine in anatomy, defines the stratigraphic range of the genus and provides recurrent ecological observations of habit and associated plants in ecotonal swamp reaches as well as in volcanic environments and on other clastic substrates. Ankyropteris may have originated from the clepsydroid zygopterid clade outside of the swamps. Ankyropteris brongniartii occurred as an epiphytic vine on Psaronius tree ferns as they expanded into coal swamps and often co-occurred with Paralycopodites even earlier in Middle Pennsylvanian. Vine stem anatomy and functional morphology of aphlebiae are emphasized in A. brongniartii with comparisons to Austroclepsis, an early “vining” false tree fern. Anatomical comparisons of Ankyropteris species based on shoots emphasize divergent habits with similar robust sizes; all exhibited aphlebiae. Known only from coal balls, Ankyropteris corrugata (Westphalian A–B) had a rampant habit on exposed peat with a succulent, dichotomous rhizome and erect fronds. The Lower Pennsylvanian specimen of Ankyropteris hendricksii is a compact tree fern with crowded frond bases and intercalated roots. Tyloses commonly occur in A. corrugata and A. brongniartii indicating water-stressed conditions. Apical meristems of shoot and fronds are reported for the first time, suggesting response growth to disturbance and rapid burial.

Coal balls were collected from four coal beds in the southeastern part of the Illinois Basin. Collections were made from the Springfield, Herrin, and Baker coals in western Kentucky, and from the Danville Coal in southwestern Indiana. These four coal beds are among the principal mineable coals of the Illinois Basin and belong to the Carbondale and Shelburn Formations of late Middle Pennsylvanian age. Vegetational composition was analyzed quantitatively. Coal-ball samples from the Springfield, Herrin, and Baker are dominated by the lycopsid tree Lepidophloios, with lesser numbers of Psaronius tree ferns, medullosan pteridosperms, and the lycopsid trees Synchysidendron and Diaphorodendron. This vegetation is similar to that found in the Springfield and Herrin coals elsewhere in the Illinois Basin, as reported in previous studies. The Danville coal sample, which is considerably smaller than the others, is dominated by Psaronius with the lycopsids Sigillaria and Synchysidendron as subdominants. Coal balls from the Springfield coal were collected in zones directly from the coal bed and their zone-by-zone composition indicates three to four distinct plant assemblages. The other coals were analyzed as whole-seam random samples, averaging the landscape composition of the parent mire environments. This analysis indicates that these coals, separated from each other by marine and terrestrial-clastic deposits, have essentially the same floristic composition and, thus, appear to represent a common species pool that persisted throughout the late Middle Pennsylvanian, despite changes in baselevel and climate attendant the glacial–interglacial cyclicity of the Pennsylvanian ice age. Patterns of species abundance and diversity are much the same for the Springfield, Herrin, and Baker, although each coal, both in the local area sampled, and regionally, has its own paleobotanical peculiarities. Despite minor differences, these coals indicate a high degree of recurrence of assemblage and landscape organization. The Danville departs dramatically from the dominance–diversity composition of the older coals, presaging patterns of tree–fern and Sigillaria dominance of Late Pennsylvanian coals of the eastern United States, but, nonetheless, built on a species pool shared with the older coals.

Ferns or fern-like plants have been important elements of terrestrial vegetation since the Late Devonian. Rhacophyton, a fern-like plant of the Late Devonian, appears to have been a colonizer of wet substrates, often forming large, nearly monotypic stands in peat-accumulating swamps. The earliest true ferns have been found in environments with high levels of disturbance, often fire, which suggest opportunistic, colonizing life histories, consistent with small, scrambling body plans. During the Early Carboniferous all major body plans and life histories of ferns appear, including scrambling ground cover, tree habit, and lianas. These ecological roles are distributed across several major lineages, including the Zygopteridales, Filicales, and Marattiales, plus some fern-like groups of uncertain affinity, and disappear and reappear independently within these groups. Until the Stephanian, the later part of the Late Carboniferous, ferns largely were confined to secondary ecological roles: colonists, understory vegetation, small vines. Beginning in the latter part of the Westphalian and expanding dramatically in the Stephanian, marattialean tree ferns became the dominant trees of tropical lowland, wetland forests. This dominance continued locally into the Permian in wetter parts of the landscape. The Paleozoic ferns suffered major extinctions at several times, beginning in the Late Carboniferous. By the Permian, new lineages were appearing, some of which would persist into and become dominant vegetational components during the Mesozoic. Among these lineages virtually all of the life histories and body plans that characterized Paleozoic ferns would reappear independently, plus some new kinds of organization and ecology, emphasizing the great evolutionary flexibility and responsiveness of fern-like construction and reproductive biology.

Pennsylvanian-age wetland plant communities and landscape gradients exhibit persistent species composition and ecomorphic structure. Such patterns are attributable in large part to strong phylogenetic partitioning of ecological resource space at the level of higher taxa. Each of four major class-rank clades in tropical wetlands was centered in a physically distinct part of the lowland ecosystem. Once established in these physical settings clades tended to resist displacement until removed by physically driven extinction. Lycopsid trees were the principal dominants of the wettest habitats and had subpartitioned these environments along generic lines. Seed plants were the dominants on well to poorly drained clastic substrates, a diverse set of habitats reflected in high diversity of species and architectures. Sphenopsids were most abundant in aggradational environments subject to high levels of physical stress. Ferns initially were interstitial opportunists and colonizers of disturbed areas in a variety of environments. These ecological patterns were established in concert with the architectural radiation of the vascular plants, which occurred during the Devonian-Mississippian transition and established the major classes. Within the wetlands, the replacement of species by close relatives drawn from the same families or genera contributed significantly to persistence of communities and landscape gradients. Replacement was more likely to occur from within a clade where similar ecologies already existed, than from across major clades between which the basic ecologies were different. Possibly interacting with the phylogenetic factors were community and landscape level multispecies effects that may have placed limits on species replacement patterns. The existence of such emergent properties of multispecies assemblages is suggested by a breakdown of the system beginning with major, climatically induced extinctions at the Middle-Late Pennsylvanian transition. Following extinctions of the major Middle Pennsylvanian trees, opportunistic ferns gave rise to dominants in many parts of the wetlands, perhaps due to loss of some aspects of system self-regulation. As climatic drying continued seed plants began their largely passive rise to dominance in most kinds of habitats.

Although the prevalence or even occurrence of insect herbivory during the Late Carboniferous (Pennsylvanian) has been questioned, we present the earliest-known ecologic evidence showing that by Late Pennsylvanian times (302 million years ago) a larva of the Holometabola was galling the internal tissue of Psaronius tree-fern fronds. Several diagnostic cellular and histological features of these petiole galls have been preserved in exquisite detail, including an excavated axial lumen filled with fecal pellets and comminuted frass, plant-produced response tissue surrounding the lumen, and specificity by the larval herbivore for a particular host species and tissue type. Whereas most suggestions over-whelmingly support the evolution of such intimate and reciprocal plant-insect interactions 175 million years later, we provide documentation that before the demise of Pennsylvanian age coal-swamp forests, a highly stereotyped life cycle was already established between an insect that was consuming internal plant tissue and a vascular plant host responding to that herbivory. This and related discoveries of insect herbivore consumption of Psaronius tissues indicate that modern-style herbivores were established in Late Pennsylvanian coal-swamp forests.

We document the presence of the piercing-and-sucking functional feeding group and the dietary targeting of vascular tissue (phloem and xylem) in marattialean tree-fern rhachises from a Late Pennsylvanian (302 Ma) coal-swamp forest in the Illinois Basin. Our evidence originates from permineralized peat that exhibits cellular-level preservation of tissues from whole Psaronius tree-fern rhachises; it includes 3 stylet probes, each of which traverses epidermal tissues and parenchyma, and terminates in a distinctive feeding cavity within phloem and xylem of a vascular strand. The stylet probes are lined with an opaque, sheathlike material, and are principally intracellular, although large gum sac cells are avoided. One of their most diagnostic features is 1 or 2 ridges occurring on the inner surface of each stylet probe, paralleling most of the probe length. These ridges, documented by light and scanning electron microscopy, are interpreted as host tissue casts of interstyletal sulci. From these and other features of stylet-trace morphology, we conclude that the herbivore was an insect of the order Palaeodictyoptera rather than an hemipteroid insect. Well developed reaction tissue surrounding the stylet trace developed while the plant host was alive, demonstrating herbivory. Previous studies have documented piercing-and-sucking in several examples of plant damage from the Early Devonian to Late Pennsylvanian (395–290 Ma). The oldest credible examples are plant lesions indicating piercing-and-sucking arthropods from 2 Lower Devonian deposits. We hypothesize that in later Middle Pennsylvanian, equatorial, coal-swamp forests of Euramerica, the dominant arborescent plants possessed vascular tissues largely unavailable to insects, because they were either deeply embedded in thick cortical tissues or protected by outer indurated, peridermal tissues. Subsequent tree-fern forests of the Late Pennsylvanian provided accessible vascular and other tissues to surface-dwelling insects with stylate mouthparts–a condition which continued into the Permian and propelled the hemipteroid radiation.

The dominant plants of the Late Carboniferous lowland tropics were taxonomically and structurally distinct from those of any later time periods. Dominance was distributed among lycopsids, ferns, sphenopsids, pteridosperms and cordaites, and each of these groups had distinctive and different ecological preferences and amplitudes. Peat-forming habitats were dominated by lycopsids throughout the Westphalian, with a significant cordaitean element in the middle Westphalian; during the Stephanian tree ferns were dominant, following major extinctions near the Westphalian-Stephanian transition. Each of the major plant groups had distinctive architectures and tissue composition. Trees contributed up to 95% of the peat biomass and tree forms of lycopsids. Psaronius and Medullosa lack good modern analogues. The cordaites were the only woody plant group to contribute significantly to peat, and then only during the mid-Westphalian. Structurally wood-like lycopsid bark is the major “woody” tissue encountered in most Westphalian coals. Tree ferns and pteridosperms were largely parenchymatous in construction; the stigmarian root systems of lycopsids also were largely parenchymatous. The tissue structure of these dominant plant suggests the need for extreme caution in the inference of mire ecological conditions or vegetational structure from coal petrographic data. Peat formed under arborescent ferns or pteridosperms, or peat repeatedly exposed to decay and rerooting by stigmarian root systems of lycopsids, would have a distinctly non-woody signature and yet would have formed in a forested environment. A summary is presented of the autecology and synecology of mire plants, emphazing the structural framework provided by lycopsids during the Westphalian. Certain constraints in the links between peat biomass and miospore palynology are discussed in terms of over-representation, under-representation and non-representation. The formulation of Smith's four-phase hydroseral model is discussed and compared with more recent data available from plant paleoecology. The current debate over an ombrotrophic vs. rheotrophic origin of Late Carboniferous peats relies in large part on paleobotanical data, almost entirely palynological, in combination with petrographic analyses. Ecological studies of miospores and of coal-ball and compression macrofossils, and the linkage of miospores to source plants, permit the re-evaluation of mire successional models. Evidence for tree lycopsids, sphenopsids, pteridosperms and cordaites suggests growth mainly in rheotrophic mires. Tree ferns are likely candidates for growth in domed mires, although evidence is ambiguous and some tree ferns clearly grew under rheotrophic conditions. Densospores, produced by at least Sporangiostrobus lycopsid subtrees, have been considered diagnostic of ombrotrophic conditions; abundant evidence refutes this simplistic interpretation and suggests broad ecological amplitudes for densospore producers, including growth under rheotrophic conditions. Although plant fossils alone can not resolve most of the major debates in modern coal geology, paleobotany does contribute significantly to our understanding of ancient mires. An approach combining paleobotanical data with petrography, sedimentology and geochemistry, on a case by case basis, is most likely to produce a clear picture.

Carbonate concretions containing permineralized peat, commonly called coal balls, were encountered in the Amburgy coal, a generally low-ash (9.4%), but commonly high-sulfur (3.6%), Middle Pennsylvanian coal of the Eastern Kentucky Coal Field. These are the first coal balls from the Amburgy coal, and one of only a few reported occurrences from the central Appalachian Basin. The coal balls occur in the upper part of the coal, between two paleochannel cutouts at the top of the Pikeville Formation, and immediately beneath a scour with a marine fossil lag at the base of the Kendrick Shale Member, Hyden Formation. The coal is thickest (1.3 m) in a narrow (

Although oribatid mites are essential to the decomposition of plant tissues in modern temperate forests by assisting conversion of primary productivity to soil organic matter, little is known of their paleoecologic history. Previously there has been scattered and anecdotal evidence documenting oribatid mite detritivory in Pennsylvanian plant tissues. This study evaluates the incidence of oribatid mite damage for seven major coal-ball deposits from the Illinois and Appalachian sedimentary basins, representing a 17 million year interval from the Euramerican tropics. Although this interval contains the best anatomically preserved plant tissues with oribatid mite borings in the fossil record, coeval oribatid mite body-fossils are absent. By contrast, the known body-fossil record of oribatid mites commences during the Middle Devonian, but does not reappear until the Early Jurassic, at which time mite taxa are modern in aspect. All major plant taxa occurring in Pennsylvanian coal swamps, including lycopsids, sphenopsids, ferns, seed ferns and cordaites, were consumed by oribatid mites. Virtually every type of plant tissue was used by mites, notably indurated tissues such as bark, fibrovascular bundles and especially wood, as well as softer seed megagametophytic and parenchymatic tissues within stems, roots and leaves. Significant evidence also exists for secondary consumption by mites of tissues in macroarthropod coprolites. Our data indicate that oribatid mites consumed dead, aerially-derived plant tissues at ground level, as well as root-penetrated tissues substantially within the peat. Oribatid mites were important arthropod decomposers in Pennsylvanian coal swamps of Euramerica. The wood boring functional-feeding-guild was expanded by insects into above-ground, live trees during the early Mesozoic. New food resources for insect borers resulted from penetration of live tissues such as cambium and phloem, and the invasion of heartwood and other hard tissues mediated by insect-fungus symbioses. Termites and holometabolous insects were prominent contributors to this second wave of wood-boring, exploiting gymnosperms and angiosperms as both detritivores and herbivores. An earlier emplacement of oribatid mites as detritivores of dead plant tissues continued to the present, but without a documented trace-fossil record.

Late Pennsylvanian coal swamps of the Illinois Basin were dominated by Psaronius tree ferns with a spatially heterogeneous distribution of medullosan pteridosperms (subdominant), calamites, sigillarian lycopsids, and cordaites. Miospore and coal-ball plant assemblages from the Missourian-age Bristol Hill Coal Member (Bond Formation) and Friendsville Coal Member (Mattoon Formation) of southeastern Illinois were quantified to analyze vegetational patterns in Late Pennsylvanian peat swamps and to compare vegetational composition of the coals. In the Bristol Hill Coal (95 coal balls, 2613 cm 2 coalball peels), tree ferns are dominant (75.6%), followed by pteridosperms (11.5%), lycopsids (10.6%), sphenopsids (0.6%), small ferns (1.6%), and cordaites (0.1%)

The comparative ecologies of Diaphorodendron, Lepidodendron, Lepidophloios, Paralycopodites (= Anabathra), and Sigillaria in Late Carboniferous coal swamps serve as a context for assessing life cycles and exploring possible structure-function relations. The distinctive aspects of the «lycopsid tree habit» in lepidodendrids are emphasized as part of the arborescent reproductive architecture of relatively short-lived (10-15 years) plants (...)

The Secor Coal of Oklahoma (Boggy Formation, lower Desmoinesian/Westphalian D equivalent) is one of the few coals discovered, to date, in which Anabathra pulcherrima (=Paralycopodites brevifolius) was a dominant element. Anabathra and Lepidophloios define the major assemblages in the coal, which also contains elements of medullosan pteridosperms and Cardiocarpus spinatus producing cordaites. The Lepidophloios to Medullosa gradient is not obscured by the numerous Anabathra-dominated zones, and a disturbance element is suggested in association with Anabathra abundance. Comparison of the coal-ball flora with a clastic-compression flora from the roof of the coal reveals widely divergent patterns of dominance and diversity. The compression flora is strongly dominated by medullosan pteridosperms with subdominant marattialean tree ferns. As in most instances, the compression flora from the immediate roof of the coal is not an accurate representation of the peat-forming vegetation, at either the level of species composition or the relative abundance of major groups of plants. The swamp and surrounding clastic deltaic environments were edaphically distinct and supported separate floras between which there was limited species exchange.

Abiotic stress has played a major role in the evolution of vascular plants by creating or delimiting habitats with low interspecific competition. These are, in effect, opportunities for survival of divergent phenotypes through non-adaptive evolution. The patterns and processes associated with stress-related evolution lend support to concepts of evolution as a process with a distinct hierarchy of levels. There are two fundamental forms of abiotic stress. Extrinsic stress is induced by an external agent(s) that impinges on ecosystems, altering conditions and leading to selection against indigenous forms; these are aperiodic or have long return times and are thus beyond the limits of adaptation. Intrinsic stress is caused by physical, usually edaphic conditions of certain kinds of habitats that select against almost all plants. These kinds of stress are fundamentally different from “stress” induced by competition or intracommunity, short-period disturbance. Extrinsic stress induces differential migration and extirpation/extinction as proximate effects. Evolution is a by product of disrupted communities in which momentary opportunities for divergence are created. The fossil record provides most of the critical sequences recording the effects of extrinsic stress. Evolution in stressed ecosystems is a “sweepstakes”, with colonizers/dispersers and preadapted forms speciating the most and gaining the greatest ecological advantage during these episodes. Extrinsic stress has been of extreme importance in shaping the phylogenetic tree of vascular plants by progressively and sequentially pruning clades from the role of ecological codominance. Intrinsically stressful environments are bounded by asymmetrical ecotones. Entry to these habitats is made possible by preadaptation. They generally are low diversity “species sinks” with highly specialized floras, rarely sites of evolutionary innovations that subsequently spread into non-stressful habitats. Due to limited species exchange with surrounding environments, these kinds of habitats tend to become progressively more archaic through time, preserving a flora that changes little for long periods. They are very susceptible to mass extinction and vegetational reorganization, at which point the cycle of increasing archaicism is reset. They appear to be good analogs for the initial phases of “adaptive” breakthrough in general, and strongly suggest a highly stochastic process. Competition-mediated adaptive evolution may hone morphologies created during periods of non-adaptive cladogenesis. The fossil record provides primary data and permits testing of theories by evaluation of predicted patterns versus empirically-determined patterns.

Two specimens of Stelastellara are described from Middle Pennsylvanian age coal balls from mid-continent United States. The stellate main axis of both specimens has a solid, exarch, actinostele with elliptical to circular bordered pitting, secondary growth and a distinctive cortex with differential thickenings. One axis is assigned to S. parvula ; it divides sympodially at one end into four typical S. parvula axes. A second specimen described as a new species, S. baxteri , is 6 mm in diameter, highly stellate with primary xylem ribs extended radially up to 1.25 mm and with radially elongate and thickened cortical cells. Along the 5 cm length, seven endogenous structures are produced, mostly from one face. The axes are largely root-like and the morphological alternatives are considered. A gymnosperm affinity is suggested. The peculiar anatomy of the root-like axes and lack of in situ evidence suggest the possibility of some kind of a perched habit.

Improved regional and interregional stratigraphic correlations of Pennsylvanian strata permit comparisons of vegetational changes in Euramerican coal swamps. The coal-swamp vegetation is known directly from in situ coal-ball peat deposits from more than 65 coals in the United States and Europe. Interpretations of coal-swamp floras on the basis of coal-ball peat studies are extended to broader regional and stratigraphic patterns by use of coal palynology. Objectives of the quantitative analyses of the vegetation in relation to coal are to determine the botanical constituents at the peat stage and their environmental implications for plant growth and peat accumulation. Morphological and paleoecological analyses provide a basis for deducing freshwater regimes of coal swamps. Changes in composition of Pennsylvanian coal-swamp vegetation are quire similar from one paralic coal region to another and show synchrony that is attributable to climate. Paleobotany and paleogeography of the Euramerican province indicate a moist tropical paleoclimate. Rainfall, runoff and evapotranspiration were the variable climatic controls in the distribution of coal-swamp vegetation, peat accumulation and coal resources. In relative terms of climatic wetness the Pennsylvanian Period is divisible into five intervals, which include two relatively drier intervals that developed during the Lower-Middle and Middle-Upper Pennsylvanian transitions. The climate during Early Pennsylvanian time was moderately wet and the median in moisture availability. Early Middle Pennsylvanian was drier, probably seasonally dry-wet; late Middle Pennsylvanian was the wettest in the Midcontinent; early Late Pennsylvanian was the driest; and late Late Pennsylvanian was probably the wettest in the Dunkard Basin. The five climatic intervals represent a general means of dividing coal resources within each region into groups with similar botanical constituents and environments of peat accumulation. Regional differences in basinal geology and climate were significant variables, but the synchronous control of paleoclimate was of primary importance.

A B S T R A C T The pteridosperm (Medullosaceae) pollen organ Sullitheca dactylifera gen. et sp. n. is described from middle Pennsylvanian coal balls. The proximally fused units of the obpyriform compound synangium separate and extend distally as finger-like projections. Each projection contains 4-6 vertically oriented cylindrical sporangia arranged in pairs along the radius of the unit; each unit extends from the outer cover wall toward the center. The distal portion of the compound synangium is hollow as a result of the lateral separation of the centripetally and distally directed synangial units. About 40 tubular sporangia are present in all and dehiscence occurs along a lateral slit in each sporangium. Vascular strands are disposed around the periphery of the organ in addition to a single strand paralleling each sporangium. Two- or threecell trichomes and stomata are present on the organ surface. Pollen of the Monoletes type is present. A paired row of sporangia in Sullitheca composing a synangial unit is considered the homologue of a paired row of sporangia in the more compact and highly evolved genus, Dolerotheca.

Quantitative analysis of Pennsylvanian coal-swamp vegetation provides a means of inferring organization and structure of communities. Distribution of these communities further provides inferences about environmental factors, including paleoclimate. Our observations are based on in situ, structurally preserved peat deposits in coal-ball concretions from 32 coal seams in the eastern one-half of the United States and from several seams in western Europe and on spore assemblages from more than 150 seams. There were three times of particularly significant and nearly synchronous vegetational changes in the Midcontinent and Appalachian coal regions during the Pennsylvanian Period. Each was different in kind and magnitude. The first marked changes occurred during the early part of the Middle Pennsylvanian with the fluctuating decline in the high level of lycopod dominance. The abundance of cordaites increased. There was a rise in the occurrences of the lycopod herbs to form intercalated marshlands and an overall increase in floral diversity. Changes ensuing from this time also include shifts in dominant species of lycopod trees and a sustained rise in abundance and diversity of tree-fern spores. The next significant time of change was during the middle part of the Middle Pennsylvanian, representing both a culmination of earlier trends and expansions of cordaites in the Midcontinent where there was a maximum change in species without net loss of diversity. Tree ferns and medullosan pteridosperms attained subdominant levels of abundance and diverse lycopod species dominated except in the Atokan-Desmoinesian transition of the Midcontinent. The third and sharpest break occurred near the Middle—Late Pennsylvanian boundary when extinctionsof the dominant, coal-swamp lycopods allowed development of tree-fern dominance. The Late Pennsylvanian coal swamps apparently were colonized or recolonized mainly by species from outside coal swamps rather than by the survivor populations of the Middle Pennsylvanian swamps. Paralleling the changes in floras through the Pennsylvanian are changes in preservational aspects of the peat. These include a decline in shoot/root ratios from approximately 1 to

Permineralized specimens of Polysporia are described from coal balls of three Middle Pennsylvanian age coals of the Illinois Basin. Identification is based on the presence of Endosporites microspores and Valvisporites megaspores along with sporangial fragments in the axils of leaves interpreted as sporophylls. The shoots exhibit alternating fertile and vegetative zones. Vegetative leaves are larger than sporophylls which are often desiccated and folded back against the stem surface; a short zone of transitional sterile leaves is found between vegetative and spore-bearing zones. Ligule pits are present on the adaxial surface of vegetative leaves. The stems are essentially herbaceous but robust and 4–6 cm in diameter. Small amounts of periderm and wood were produced but primary tissues were not disrupted. Polysporia is the first herbaceous lycopod with an alternation of fertile and vegetative areas found in Pennsylvanian peats and is compared with Spencerites, Sporangiostrobus, and Lepidodendron dacrydioides (proposed vegetative stem of Sporangiostrobus) which are suspected to have similar structure. The rarity of Polysporia in coal balls and its frequent associations with Sphenophyllum, combined with low numbers of arborescent lycopods, Psaronius or Medullosa, suggest an environment of growth not frequently encountered in coal-ball studies of the swamps. Polysporia may have grown in marginal wetland environments where herbaceous and low shrubby plants predominated; this suggests that some Endosporites—rich coals of the Upper Pennsylvanian are derived in large part from marshland peats.

A new lyginoptend pollen organ is described based upon specimens occurring in a single coal ball from the Providence, Kentucky locality. Seven to nine beaked sporangia are fused together at their proximal ends forming a common synangial chamber; synangia are joined together in clusters of two or three. In situ prepollen is similar to Cyclogranisporites and Verrucosisporites sporae dispersae. The thick exine has a lamellate nexine and a prominent alveolate sexine.

A new species of Psaronius is described from permineralized monocyclic stems with distichous leaf scars. Diameters for the steles are 3.5–4.4 cm, up to 6.5 cm for the stem, and 8 cm for the trunk which includes inner and outer roots; the longest of 11 specimens is 32 cm. These specimens from the lower Pennsylvanian of western Illinois are the oldest known histologically preserved stems and roots for the genus. Psaronius simplicicaulis sp.nov., with its distichous leaf arrangement, is very similar to Mississippian – early Pennsylvanian Megaphyton specimens, indicating that the earliest known marattialean tree ferns were smaller in diameter than their late Pennsylvanian relatives and probably monocyclic with distichous fronds. The middle Pennsylvanian increase in the distribution and abundance of Psaronius generally coincides with increased size, polycyclic stelar anatomy, and polystichy.

DiMichele, W.A. and Phillips, T.L., 1988. Paleoecology of the Middle Pennsylvanian-age Herrin Coal swamp (Illinois) near a contemporaneous river system, the Walshville paleochannel. Rev. Palaeobot. Palynol., 56: 151-176. Coal-ball peats were sampled quantitatively in seven profiles from the Old Ben Coal Company No.24 Mine in southern Illinois. The coal and the coal-ball peats are thicker in this near-channel area than at any site sampled so far. Lycopods dominate the peat-swamp flora, as at other Herrin Coal sites, with Lepidophloios hallii being the most important (30-78% of whole-profile peat biomass). Ferns (5-15% biomass), and pteridosperms (1 15% biomass), also are important in the swamp flora. Shoot-root ratios in profiles are relatively high, 1.4 2.8. Fusain abundance is concentrated in several mid-seam zones (above the blue-band clastic parting) with the highest pteridosperm abundances. Three major plant associations ("communities") are detected by multivariate analyses. The most common assemblage is dominated by Lepidophloios hallii ( > 70% of biomass), with low-diversity and little representation of ground-cover and free-sporing plants; this is interpreted as representative of standing-water, high abiotic-stress conditions. Lepidophloios assemblages are common in all profiles. Diaphorodendron scleroticum and D. dicentricum characterize a second assemblage (> 20% of biomass) that can include a diversity of species and growth forms; these associations appear to be structured by disturbance. Diaphorodendron is most abundant just above the seat earth and in several consecutive zones near the top of the seam. Medullosa (>20% biomass) characterizes the third major assemblage; Medullosa assemblages are most common at the base of the seam, in proximity to the blue-band clastic parting, and in a mid-seam interval of "dirty" coal. The association of MeduUosa with zones of > 107/o fusain and abundant mineral matter suggests alternation of flooded and dry conditions. Psaronius tree ferns form an overprint on these distributions, occurring widely in all but Lepidophloios.dominated assemblages.

Euramerican coal-swamp plants are anatomically preserved in an upper Visean to Westphalian A (mid-Carboniferous) volcanogenic sequence in the Tazekka massif, northeastern Morocco. The peat assemblage occurs in siliceous inclusions resembling coal-ball deposits and consists of the lycopod tree Lepidophloios with Lepidocarpon , lyginopterid seed ferns with Lagenostoma ovules and Botryopteris , a fern. These plants are consistent with a Namurian to Westphalian A age but are not stratigraphically indicative of a more precise age determination. The taxa and their paleoecology are indicative of a paleotropical location for part of Morocco in the Euramerican coal belt and consequently relevant to proposed fits of Morocco in Pangaean paleogeography.

The vegetation of many Euramerican coal swamps is known from coal-ball peats in the tropical rainy zone across the paleocontinent of Laurussia in the Upper Carboniferous. The stratigraphic occurrences of coal balls in Europe (lower Westphalian) and in North America (upper Westphalian and lower Stephanian) are largely complementary and a revised correlation chart is given. Quantitative analyses of the vegetation from these autochthonous peats are combined with coal palynology to determine on overview of swamp vegetation patterns during the Westphalian and early Stephanian. In comparison to the dominance and great diversity of pteridosperms in the Upper Carboniferous compression floras, seed ferns were minor to subdominant elements in the coal-ball peats. The quantitative composition of organ assemblages of the principal pteridosperms is given with stratigraphic occurrences of Medullosa and Sutcliffia (Medullosaceae), Heterangium, Lyginopteris, Microspermopteris , and Schopfiastrum (Lyginopteridaceaea) and Callistophyton (Callistophytaceae). The major peat contributors among pteridosperms are Lyginopteris (⩾90%) in the Westphalian A and Medullosa (⩾95%) in the Westphalian D and Stephanian. Lyginopteris became extinct in the early Westphalian B and Medullosa became abundant during the Westphalian C–D transition and a subdominant in the Stephanian contributing 13–21% of the permineralized peats. Paleoecological interpretations indicate that medullosan trees were most abundant but patchy in distribution in drier swamp stages with enriched nutrients and near major channels in swamps during the Westphalian D. It is suggested that the swamp pteridosperms are probably quite similar to or identical with some of the representatives in the more diverse compression floras. The evolution and diversity noted in swamp pteridosperms are considered principally the product of adjacent lowland communities which repeatedly introduced seeds into the wetlands. The swamp pteridosperms exhibit the greatest fluctuation in abundance (biomass) from site to site in the same coal, probably the highest level of diversity and the only steady pattern of increase in importance during the Late Carboniferous with the possible exception of the Westphalian B–C interval. The close relationships inferred between swamp pteridosperms and their lowland seed sources are also compatible with the frequent association of tree ferns and seed ferns during the Westphalian D and in the Stephanian when these two kinds of frond-bearing trees formed most of the vegetation in both lowland and swamp environments.

Petrifactions of Rhacophyton ceratangium were collected from the Upper Devonian Hampshire Formation near Valley Head, West Virginia. The approximate age of the locality is latest Cassadagan to earliest Bradfordian, equivalent to the upper middle Famennian (Fa2c) in European terminology. Ground thin sections were prepared from the limonitized petrifactions, and a pyritized specimen was prepared and examined under the SEM. The rachides of R. ceratangium were found to be bipolar or clepsydroid in cross-section, with secondary xylem present or absent. Vascular rays in the secondary xylem are demonstrated in this species for the first time. Pitting of tracheids was found to be scaliformly bordered. Emission of pinna traces was found to be etapterid. Peripheral loops, when present, were filled with parenchyma, or replaced by a decay gap or lacuna. Pinna traces bifurcate at an early stage in their development, and the clepsydroid anatomy is repeated in at least one order of branching. R. ceratangium was compared to the other anatomiccally known species within the genus.

The reproductive organization and function of heterosporous arborescent lycopods in the Carboniferous are categorized based on histologically preserved specimens: free-sporing bisporangiate cones of the Lepidostrobus type (sensu stricto) which includes Bothrodendrostrobus, Sporangiostrobus and Polysporia; monosporangiate cones with intrasporangial modification, the Mazocarpon type; megasporangium—sporophyll modification of the monosporic, dispersed Achlamydocarpon type; and the integumentary type represented by Lepidocarpon. The taxonomy—morphology of each type of megasporophyll unit is summarized; their gametophytes and embryo stages are described and illustrated. Lycopod reproductive biology is related to swamp environments and their changes in the Pennsylvanian. The morphological and functional seed-like aspects of Achlamydocarpon and Lepidocarpon are considered aquatic adaptations, partially reflecting in their sporophyll design the leaf-cushion potentials of Lepidodendron and Lepidophloios.

Evidence is presented for the earliest known occurrences of non-vascular land plants and of higher, septate fungi. Macerates of carbonaceous silstone lenses from the lower Massanutten Sandstone, early Silurian (Llandoverian) of Virginia, have yielded a diverse assemblage of microfossil elements. Parallel aligned, banded tubes with annular to spiral ribbing and rounded to papilliform ends, membranous cellular sheets, cuticles, trilete spores, small spore tetrads, and septate higher filamentous fungi were recovered from the macerates. The banded tubes are probably a significant analogue with supportive or conductive cell types, but are not considered tracheidal. The heterogeneous plant assemblage may represent a thalloid, non-vascular land plant, in part, with a tubular-filamentous (nematophytic) organization associated with a membranous cellular layer and cuticular covering. While no spores were established as nematophytic, the presence of trilete spores adds to the indirect evidence of multiple evolutionary convergence toward land-plant characters. This assemblage is interpreted as of land-plant origin, based on the inferred fluvial depositional model of the fossiliferous rocks. A glacio-eustatic sea-level drop in the late Ordovician is suggested as a stimulus to the advent of land plants in the early Silurian.

Archaeopteris specimens were collected in the summer of 1962 from Upper Devonian rocks at the head of Goose Fiord, Ellesmere Island, Arctic Canada. The collections include two species: A. fissilis and A. obtusa. The fertile parts of the former are described in detail; the pinnules bear two rows of sporangia which are about 2 mm long, dehisce longitudinally, and probably were homosporous. Stem impressions are abundant in the entire area and it is evident that extensive forests existed here in Upper Devonian times. A few well-preserved roots with typical Callixylon anatomy were found associated with the fronds.

A B S T R A C T The basal stem anatomy of three young sporophytes of Psaronius from the Middle Pennsylvanian of Kansas and Illinois is described. The origin of the second stelar cycle is demonstrated in the transition from a simple, amphiphloic siphonostele to a dicyclic dictyostele. Petioles with C-shaped vascular strands are attached to the stem in a one-third phyllotaxy. A root mantle is lacking. Basal stem anatomy of Psaronius is compared with that of living genera of the Marattiaceae. ONTOGENETIC approaches to the study of Pennsylvanian-age plants have greatly increased our understanding of the arborescent lycopods, calamites, seed ferns, and tree ferns. Although some fossil apices have been described, the fragments usually represent more mature parts of the plaint, and in many cases secondary growth has further modified the plant body. These studies have been reviewed in detail by Delevoryas (1964). For the first time small, young sporophytes of Psaronius, a marattiaceous tree fern, have been discovered with attached petioles in Pennsylvanian-age coal balls from Illinois and Kansas. Some of the earliest ontogenetic stages of the vascular system are described below.

Data are given on the vertical distribution of Protosalvinia arnoldii, P. ravenna and P. furcata from vertical samples of the New Albany Shale of Kentucky. Thalli of each of the three species are described and interpreted ontogenetically with P. arnoldii, P. ravenna and P. furcata forming an ontogenetic series in that order. Thalli of the three species occur largely in three successive zones and each constitutes more than 90% of the specimens of a zone. The inverted depositional order of the ontogenetic sequence is interpreted as a successively juvenile series resulting, in part, from the repeated modification of their littoral habitat, such as drowning by a transgressing sea, which has permitted survival of successively earlier but not later stages. Branched forms of P. arnoldii from Kentucky and of P. ravenna from Tennessee are reported for the first time. The distinctions between Protosalvinia and Foerstia are discussed. The affinities of Protosalvinia with the Phaeophyta, particularly with the Fucales, are considered.

A new species of Rhacophyton, R. ceratangium, is described from Upper Devonian rocks of West Virginia, U.S.A.; this is synonymous with R. incertum (Dawson) Krausel and Weyland but reasons are cited to indicate that the latter species name is not appropriate. The collections include: stems up to 2 cm in diameter bearing bipinnate, non-laminate vegetative fronds; abundant well preserved fertile fronds that show clearly the distinctive morphology of their sterile and fertile pinnae; fragments of axes with woody tissues petrified. The sporangia are particularly distinctive with their long slender tip; they dehisced longitudinally and contained several hundred spores; all available evidence indicates that the plant was homosporous. All petrified axes have a slender bar-shaped strand of primary wood swollen at either end and surrounded by strongly developed secondary wood consisting of scalariform tracheids and rays. R. ceratangium is closely related to the Belgian R. zygopteroides Leelercq. A comparison with other Devonian and Carboniferous pteridophytes suggests that Rhacophyton is probably a primitive member of the Progymnospermopsida or immediately ancestral to that group.

Coal palynology and studies of petrified peat indicate major changes in coal-swamp floras and the botanical constituents of coal throughout Pennsylvanian time. The changes are the result of broad climatic shifts and local environmental factors. The most striking is the change from a lycopod-dominated flora to one in which tree ferns were the major element. This change occurred at the Desmoinesian-Missourian (Westphalian-Stephanian) boundary and is probably multicontinental in scope.

The morphological and paleogeographic evidence suggesting that cordaitean-dominated swamps from the early Westphalian D (= 295 m.y.b.p.) of Iowa grew in salt water swamps is reviewed. Cordaitean trees, Psaronius tree ferns, and Medullosa seed ferns contributed 95% of the peat in coal-ball samples taken from three Iowa mines. Ordination analysis shows that associations dominated by Psaronius and Medullosa succeeded an association dominated by cordaitean trees at each site. Based on comparisons with Upper Carboniferous compression flora deposits, Psaronius and Medullosa seem to have grown in freshwater or only slightly brackish water habitats. The root morphology of cordaitean trees from Iowa and the paleogeographic position of these swamps suggest that cordaitean trees which produced Nucellangium glabrum and Cardiocarpus spinatus seeds grew in salt water. Results of the ordination analysis suggest that cordaitean trees which produced Mitrospermum seeds grew in freshwater or only slightly brackish habitats. The methods used to assess these deposits as mangrove peats can be applied to any structurally preserved peat. Most other putative mangrove communities in the fossil record have been described from compression-flora deposits. The non-morphological criteria for assessing these floras as mangrove swamp deposits are reviewed.