William DiMichele

Although conceptual whole-plants are occasionally reconstructed, disarticulation means that palaeobotanical taxonomy remains primarily the preserve of fragmented organ-species, each bearing a Linnaean binomial. Thus, a "natural" taxon that would in any neobotanical classification bear a single valid binomial (any other epithets automatically being deemed synonyms) typically is a chimera, consisting of several binomials that are not only valid but also arguably essential, each representing a different organ of the original plant. The situation is further complicated by the fact that each organ can also carry multiple valid binomials that refer to contrasting preservation states, most commonly either adpression or permineralisation. Thus, a fossil plant is obliged to carry the heavy burden of not one but two or more parallel taxonomies. The two opposing logical approaches to clarifying this complex situation are (1) to coin additional formal names for organ-species that are found in multiple modes of preservation but at present are named in only one mode, or (2) to attempt to gradually rationalise parallel preservational taxonomies through detailed character comparison, giving priority to whichever preservational mode typically offers a stronger suite of morphological characters and therefore the greater probability of approaching the biological reality necessary for meaningful evolutionary and ecological interpretation. We illustrate our preference for Option 2 using Palaeozoic rhizomorphic lycopsid genera in general and our antagonism to the recently erected permineralisation stem-genus "Dimicheleodendron" in particular.

In our recent description of a new genus of lycopsids from the Carboniferous (Pennsylvanian), Synchysidendron DiMichele & Bateman (1992), we neglected to designate the type of the generic name. Under Art. 37.1 of the botanical Code, on or after 1 Jan 1958, the name of a new taxon is not validly published unless the (holo) type is indicated. Without valid publication of the generic name, our species names were also not validly published under Art. 43.1.

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

Breathtaking in scope, this is the first survey of the entire ecological history of life on land—from the earliest traces of terrestrial organisms over 400 million years ago to the beginning of human agriculture. By providing myriad insights into the unique ecological information contained in the fossil record, it establishes a new and ambitious basis for the study of evolutionary paleoecology of land ecosystems. A joint undertaking of the Evolution of Terrestrial Ecosystems Consortium at the National Museum of Natural History, ...

ABSTRACT—In 1904, Clarence Luther Herrick described a lycopsid flora (including three new species of Lepidodendron) from “fire clay” of Pennsylvanian age being mined for brick manufacturing east of Socorro. Herrick’s description of the locality was vague, and it has not been revisited in nearly a century. In 2002 we relocated Herrick’s locality. The “fire clay” is a refractory gray to black shale in the lower part of the Middle Pennsylvanian (Atokan) Sandia Formation that can be followed on strike through a series of fault blocks for more than 2 km. The Sandia Formation at the lycopsid locality contains basal troughcrossbedded quartzose sandstone and quartzite-pebble conglomerate about 4 m thick, filling channels scoured into Proterozoic granite. These coarse clastics are sharply overlain by ~2.5 m of gray and yellow, fine-grained, massive to thinly laminated sandstone, which has lycopsid bark concentrated near the top. This in turn is overlain by the “fire clay” interval, ~4 m of g...

In our recent description of a new genus of lycopsids from the Carboniferous (Pennsylvanian), Synchysidendron DiMichele & Bateman (1992), we neglected to designate the type of the generic name. Under Art. 37.1 of the botanical Code, on or after 1 Jan 1958, the name of a new taxon is not validly published unless the (holo) type is indicated. Without valid publication of the generic name, our species names were also not validly published under Art. 43.1.

Premise of research. Extant Isoetes species, which all develop small pseudoherbaceous habits, are the only living remnants of the once diverse clade of rhizomorphic lycopsids, which included trees that grew to towering heights of 50 m. Although the rhizomorphic lycopsids evolved a range of diverse body plans in the Pa-leozoic, it is thought that the evolution of the small pseudoherbaceous habit, with small rooting systems similar to modern Isoetes species, was a late event in the clade's history, occurring in the Mesozoic. Here we describe small fossilized rooting systems from the early Permian Abo Formation of New Mexico, increasing our knowledge of the diversity of small Paleozoic rhizomorphic rooting systems. Methodology. Ten fossilized rooting systems are described from a slab collected from the early Permian Abo Formation of New Mexico. Pivotal results. Here we report 10 rooting systems interpreted as those of rhizomorphic lycopsids due to the presence on each of a large number of isotomously branched rootlets radiating from a central rhizomorph and two associated microphyll leaf impressions. Because of the fossils' tiny size (the largest rhizomorph is only 1.5 cm in diameter, and the largest rooting system, including rootlets, is only 6 cm in diameter), we interpret these fossils either as juvenile plants or as adult morphologies with a small rooting system. Given the paucity of mature rhizomorphic lycopsids in the Abo Formation and the limited fossil record of juvenile rhizomorphic lycopsids from any geological period, we predict that these are most likely to be adult plants with small rooting systems. Conclusions. The small size of the specimens described here increases our knowledge of the diversity of small rhizomorphic rooting systems in the Paleozoic before the radiation of the modern Isoetes growth habit during the Mesozoic.

Fossil floras have been recovered from a unique deposit of early Permian age in North-Central Texas. The site, Kola Switch, preserves three distinct floras in different lithofacies, in a succession from a single outcrop. The sedimentary environment appears to be a floodplain channel fill of primarily siltstones and claystones. The lowermost flora, preserved in a kaolinitic siltstone, indicates active water flow. It is dominated by plants typical of well-drained substrates, dominated by Sphenopteris germanica, and contains no wetland elements. The middle flora is from a finely laminated carbonaceous claystone and is dominated by marattialean tree ferns, with no elements from habitats typical of seasonal moisture availability. It contains no roots and appears to have formed as a floating peat mat. The upper flora is a mixed assemblage of wetland taxa and those typical of well-drained soil environments or a seasonal rainfall regime. Unlike the two lower floras, it has a relatively even distribution of dominance and is the most diverse of the three assemblages. Palynofloras also were recovered from each of these beds. The palynofloras, although varying between and even within the beds, indicate a common background species pool during the time interval sampled, suggesting that these distinct floras reflect local changes in microhabitat conditions under a constant climatic background. The palynoflora from each bed has characteristics in common with the macroflora of that bed, but also distinct differences. Together, the macroflora and microflora provide an unusually broad picture of this site through time. Kola Switch compares favorably with the recently described flora from the nearby Sanzenbacher Ranch site of approximately the same age and also with floras of Rotliegend age from Central Europe.

The Carboniferous, the time of Earth’s penultimate icehouse and widespread coal formation,
was dominated by extinct lineages of early-diverging vascular plants. Studies of nearest living
relatives of key Carboniferous plants suggest that their physiologies and growth forms differed
substantially from most types of modern vegetation, particularly forests. It remains a matter of
debate precisely how differently and to what degree these long-extinct plants influenced the
environment. Integrating biophysical analysis of stomatal and vascular conductivity with
geochemical analysis of fossilized tissues and process-based ecosystem-scale modeling yields a
dynamic and unique perspective on these paleoforests. This integrated approach indicates that
key Carboniferous plants were capable of growth and transpiration rates that approach values
found in extant crown-group angiosperms, differing greatly from comparatively modest rates
found in their closest living relatives. Ecosystem modeling suggests that divergent stomatal
conductance, leaf sizes and stem life span between dominant cladeswouldhave shifted the balance
of soil–atmosphere water fluxes, and thus surface runoff flux, during repeated, climate-driven,
vegetation turnovers. This synthesis highlights the importance of ‘whole plant’ physiological
reconstruction of extinct plants and the potential of vascular plants to have influenced the Earth
system hundreds of millions of years ago through vegetation–climate feedbacks

—A reassessment of the taxonomic relationships of North American gigantopterids is presented in light of an examination of large populations of specimens housed in the US National Museum of Natural History. Variations in venation and subtle aspects of leaf shape facilitate refined understanding of the relationships and diversity of the North American gigantopterid species leading to an improved understanding of the taxonomic and biogeographic relationships of this group, which are found most abundantly in western equatorial Pangea and Cathaysia. Current literature suggests that there are eight North American genera, however, this study has revealed a morphological overlap of several previously defined genera, leading to the conclusion that Gigantopteridium encompasses the species previously treated as Cathaysiopteris yochelsonii as well as a new species, Gigantopteridium utebaturianum. The transfer of C. yochelsonii to Gigantopteridium yochelsonii suggests that Cathaysiopteris may represent a genus endemic to Cathaysia, limiting the biogeographical connection between the regions to Zeilleropteris, Gigantopteridium, Euparyphoselis, and Gigantonoclea.

—Taxonomic analysis is provided for a Middle Pennsylvanian macrofloral assemblage collected from clastic wetland deposits in Clay County, Indiana, on the eastern margin of the Illinois Basin. Adpressed plant fossils were recovered from four distinct beds in the lowermost Staunton Formation, positioned above the Minshall Coal (uppermost Brazil Formation), part of a succession deposited near the Atokan-Desmoinesian boundary. The assemblage of 22 fossil-taxa is dominated by pteridosperms (including Neuropteris flexuosa, Macroneuropteris scheuchzeri, Alethopteris densinervosa, Neuropteris ovata, Eusphenopteris neuropteroides, and Neuropteris missouriensis) with lesser cordaitaleans (Cordaites spp. indet.) and sphenopsids (particularly Sphenophyllum cuneifo-lium). Lycopsids are uncommon, and ferns are rare. In contrast, the microfloral assemblage from the Minshall Coal and overlying clastic units is dominated by lycopsid and tree fern spores. Comparisons with established biozonation schemes yield different ages depending on the regional biostratigraphic framework used: (1) latest Bolsovian (Radiizonates difformis Biozone, American microfloras); (2) latest Bolsovian or earliest Asturian ('Neuropteris' rarinervis Biozone, Appalachian Basin macrofloras); or (3) earliest Asturian (Linopteris obliqua Biozone, European macrofloras). The placement and correlation of the Bolsovian-Asturian and Atokan-Desmoinesian boundaries, which have traditionally been equated by palynology, are evaluated in the context of this discordance. Several revised stratigraphic scenarios are proposed for this interval in the Illinois Basin, which is being increasingly recognized as a time of significant environmental change throughout Euramerica. Homotaxial comparisons with European macro-floral assemblages indicate that, of the 18 biological taxa recorded, between 14 and 17 (78–94%) also are common in coeval wetland deposits in Europe. The similarities exemplify the spatial conservatism and low diversity of wetland plant communities over vast areas of tropical Euramerica, a manifestation of the intrinsically stressful conditions that characterize such habitats, and indicates that neither the Laurentian Shield nor the Appalachian-Variscan Mountains were an insurmountable barrier to plant dispersal during the Middle Pennsylvanian.

A well preserved plant assemblage at the Colwell Creek Pond locality of Leonardian (Kungurian) age provides an opportunity to evaluate taphonomic conditions in a dryland alluvial setting. A narrow channel body incised to 5 m depth through red paleo-Vertisols contains 2 m of varicolored laminated mudstone with graded layers and plant material. X-ray diffraction analysis of individual laminae indicates the presence of chlorite, illite, kaolinite, and mixed-layer clay, with hematite in red and gray layers and goethite in yellow-brown laminae. No carbonate was identified, and the total organic carbon content is minimal. The fine sediment accumulated in a shallow abandoned channel from suspension and gentle underflows, probably linked to seasonal inflow, and analysis of lamina thickness suggests that standing water may have persisted for up to a few millennia. The preservation of lamination is attributed to a lack of bioturbation, possibly linked to a paucity of subsurface oxygen, low productivity, elevated salinity, rapid deposition, or a combination of these factors; minimal bioturbation may also reflect the limited use of freshwater ecospace during the Early Permian. Clay-rich paleo-Vertisols complete the fill, with drab root traces that indicate growth of vegetation in a strongly seasonal setting. Abundant plant material in the laminated beds includes branches of walchian conifers, the possible cycadophyte Taeniopteris spp., and the comioid, possible peltasperm, Auritifolia waggoneri. They were derived from an adjacent riparian zone and preserved as 3D goethite petrifactions. Much of the foliage shows evidence of arthropod herbivory. Although a humid climatic episode cannot be ruled out, the exceptional abundance and preservation of the plants probably reflects the persistence of an oxbow lake on a relatively arid alluvial plain, where riparian plants experienced periodic moisture stress but had access to groundwater nearly year round. Rapid burial in standing water, the lack of bioturbation in the laminated sediments, and early biomineralization probably explain the exceptional preservation of the plant remains.

Most of the morphological studies of late Desmoinesian age (late
Westphalian D) coal-ball plants in the Euramerican floral province have
utilized specimens from the Herrin (No. 6) Coal at the Sahara Coal
Company Mine No. 6 in southern Illinois. The compiled coal-ball flora of 59
genera and 68 identified speciesis the largest known for a single mine in the
Pennsylvanian. Quantitative analysis of coal-swamp vegetation from peat
profiles from two sites with 12 to l5 coal-ball zones, 526 coal balls, and
31,555 cm2 surface area of peels (biomass determinations) indicate that the
seam is dominated by lycopods with 63 to 65 percent of the volume; ferns
and pteridosperms are subdominants with l5 to 17 percent and 15 to 16
percent, respectively. Sphenopsids contributed 4 percent with cordaites
< 0.2 percent. The organ composition of the peat profiles is 35 to 47
percent for roots, 27 to 42 percent for stems, l7 to l8 percent foliage, and 6
to 9 percent fructifications. Lycopods and ferns are the major contributors
of roots and fructifications; lycopod stems and pteridosperm foliage are the
most abundant for those organs. On a seam basis the peat is largely
composed of these genera: Lepidophloios (29 to 49 percent), Lepidodendron
(13 to 27 percent), Psaronius (15 to 16 percent), and Medullosa (13 to 14
percent). The most complete vertical section of coal-ball zones indicates an
oscillating series of swamp environments between strongly dominated
Lepidophloios forests with low diversity and diverse forests with Lepidodendron
or rarely Sigillaria, a lower story of Psaronius and/ or Medullosa, and a
ground story of small plants. Changes in vegetation occur in relationship to
the five clastic partings in the seam. Sigillaria-Paralycopodites assemblages
with the maximum fusain content for the profile occur between the most
prominent pair of gray shale bands. Indications of two floods intervened by
an extreme dry period are compared to the "blue band." Lepidophloios
(prolonged standing water and net rising water table) and Sigillaria (driest
habitat conditions) assemblages are the extremes in polar ordination of
communities. Lepidodendron-M-edullosaa ssemblages ar variously intermediate
in habitats and are diverse. Psaronius probably exhibits the broadest
ecological amplitude. Dominance diversity curves of representative assemblages
are illustrated. The paleoecology of the two sites differs significantly
in thickness and number of coal-ball zones, relative abundances of aerial and
root composition, and percent volume of Lepidophloios and Lepidodendron scleroticum.
Beta-diversity values for the two sites are 2.4 to 3.1. The field
relations of coal-ball zones, clastic bands, major fusain and pyrite occurrences and the continuity and preservational qualities of the vegetation are
consistent with independent coal -ball formation from the bottom most coal -
ball zone upward in a recurrent series of permineralizing episodes.

Fossils found in cores from wells in the Midland Basin of West Texas include several kinds of terrestrial plants and a variety of marine animal remains. Depositional settings ranged from basin slope to deep-water basin floor, hence the presence of land plants was unexpected. The fossil plant assemblage is depauperate, dominated by Germaropteris martinsii, a Permian-age peltasperm. Other specimens include the peltasperm Supaia, Sphenopteris germanica, axes of uncertain affinity, and incertae sedis remains presumed to be terrestrial plants. Fossil plants are found predominantly in fine-grained, siliceous mudrocks between coarser-grained calcareous floatstones and wackestones/packstones interpreted as debrites and turbidites, suggesting that the plants were carried from land by surface currents before sinking to the basin floor and being buried by slowly accumulating hemipelagic sediment. Specimens were examined from drillcores in 14 wells spanning an interval from the lower Wolfcamp through the lower Leonard. This record of G. martinsii in lower Permian Wolfcamp rocks is among the earliest occurrences of these plants, which have been found most abundantly in upper Permian strata of Western Europe.

Six late Atokan (early Asturian) floras from seasonally dry environments are described and quantitatively analyzed from adpressions and palynomorphs. Collections are from the eastern margin of the Illinois Basin, USA, in an 80 km N-S transect. Plant fossils occur in sedimentary rocks below the underclay (paleosol) of the Minshall-Buffaloville Coal Member (thus, not “roof-shale” assemblages), uppermost Brazil Formation. Growth of floras under seasonal dryness is indicated by outcrop and lithological features that suggest deposition in flashy discharge streams, including intraformational conglomerates, plant fossils that cross bedding planes indicating rapid, episodic burial, and local rhythmically laminated sediments. Common charcoal clasts are consistent with seasonal climate. Cordaitalean foliage dominates the macroflora, accompanied by the dryland elements Lesleya sp., Taeniopteris sp. cf. T. multinervia, and Sphenopteridium sp. Two unusual forms of foliage are presumed to be rare or novel dryland species. Small numbers of wetland/periwetland taxa include calamitaleans, Linopteris neuropteroides, Karinopteris/Eusphenopteris sp., marattialean fern foliage, Senftenbergia plumosa, cf. Zeilleria avoldensis and Sphenopteris sp. The palynoflora is dominated by marattialean tree ferns, wetland plants with broad dispersal capacities and environmental tolerances. Subdominant elements also have strong wetland affinities: arborescent lycopsids, calamitaleans, small ferns.  Cordaitalean pollen is relatively uncommon.  Palynoflora-macroflora mismatches may reflect primary ecology, palynomorph reworking, or both.  The occurrence of these floras near the Atokan-Desmoinesian (~Bolsovian-Asturian) boundary coincides with an array of physical and geochemical data that indicate change from weak rainfall seasonality to marked seasonality at all phases of glacial-interglacial cycles reflected prominently in the stratigraphic record from the localities studied.

Saltational evolution, a much abused term, is here narrowly defined as a genetic
modification that is expressed as a profound phenotypic change across a single generation
and results in a potentially independent evolutionary lineage (prospecies: 'hopeful
monster' of Richard Goldschmidt). Dichotomous saltation is driven by mutation
within a single ancestral lineage, and can result not only in instantaneous speciation
but also in the simultaneous origin of a supraspecific taxon. Reticulate saltation is
driven by allopolyploidy and thus incorporates genes of fwo ancestral lineages; it
results in speciation only. Several exceptionally rapid but multigenerational evolutionary
mechanisms are collectively termed parasaltational. Saltational evolutionary mechanisms
probably generated many vascular plant species and most higher taxa.
Hypotheses of saltation can be falsified using cladograms, which also provide an
essential context for interpretations of evolutionary process as well as pattern - here
illustrated using studies of evolutionary developmental change in architectures of
fossil lycopsids and living angiosperms.
The neoGoldschmidtian synthesis advocated here accepts Goldschmidt's concept
of speciation across a single generation but rejects his preferred causal mechanism
of large-scale mutations and his requirement for competitively high levels of fitness
in the monsters. Rather, we postulate that vast numbers of hopeful monsters are continuously
generated by mutation of key homoeotic genes that control ontogeny via
morphogens ('D-genes' of Wallace Arthur). The fitness of hopeful monsters is inevitably
too low to survive competition-mediated selection - their establishment requires
temporary release from selection in unoccupied niches. The prospecies can then be
honed to competitive fitness by gradual reintroduction to neodarwinian selection.
When viewed backward through geological time, niches become less well-defined
and more often vacant, causing a corresponding increase in the probability of successful
establishment of hopeful monsters. Hence, saltation was most important among
the earliest land plants, explaining the Siluro-Devonian origins of all class-level taxa.
Although D-genes are similar at the molecular level across the biotic kingdoms, their
phenotypic expression differs between higher plants and higher animals; this reflects
highly contrasting modes of growth, notably the Iocalization of plant growth in
numerous meristems and consequent continuous, largely iterative development. More
importantly, the sessile life-style of plants renders competition indirect and environmentally
mediated; thus, vectorial selection is a far less profound cause of evolution
in plants than in animals. Plants enjoy much greater latitude for nonlethal experimentation
in form by saltation. Future advances in the study of evolutionary mechanisms
will require cladograms that use phenotypically expressed genes as characters, rather
than static morphology or cryptic base pairs, thereby allowing reciprocal illumination
between phenotype and genotype.

Organic carbon burial plays a critical role in Earth systems, influencing atmospheric O 2 and CO 2 concentrations and, thereby, climate. The Carboniferous Period of the Paleozoic is so named for massive, widespread coal deposits. A widely accepted explanation for this peak in coal production is a temporal lag between the evolution of abundant lignin production in woody plants and the subsequent evolution of lignin-degrading Agaricomycetes fungi, resulting in a period when vast amounts of lignin-rich plant material accumulated. Here, we reject this evolutionary lag hypothesis, based on assessment of phylogenomic, geochemical, paleontological, and strati-graphic evidence. Lignin-degrading Agaricomycetes may have been present before the Carboniferous, and lignin degradation was likely never restricted to them and their class II peroxidases, because lignin modification is known to occur via other enzymatic mechanisms in other fungal and bacterial lineages. Furthermore, a large proportion of Carboniferous coal horizons are dominated by unlignified lycopsid periderm with equivalent coal accumulation rates continuing through several transitions between floral dominance by lignin-poor lycopsids and lignin-rich tree ferns and seed plants. Thus, biochemical composition had little relevance to coal accumulation. Throughout the fossil record, evidence of decay is pervasive in all organic matter exposed subaerially during deposi-tion, and high coal accumulation rates have continued to the present wherever environmental conditions permit. Rather than a consequence of a temporal decoupling of evolutionary innovations between fungi and plants, Paleozoic coal abundance was likely the result of a unique combination of everwet tropical conditions and extensive depositional systems during the assembly of Pangea. lignin | carbon cycle | wood rot | fungi | lignin degradation

This volume presents eight articles on the Pennsylvanian-Permian geology and paleontology of the
Robledo Mountains in Doña Ana County, southern New Mexico. The reported research resulted from a federally-
funded study of the trace fossils in and around the Prehistoric Trackways National Monument (PTNM). We
divide the overview by the main topics addressed—stratigraphy, sedimentology, paleobotany, micropaleontology,
biostratigraphy and ichnology―and draw attention to the most significant research results. These indicate that the
identification of glacio-eustatically driven sedimentary cyclicity in the Robledos Lower Permian strata, paralleling
that seen in mid-continent and Appalachian basin cyclothems of Pennsylvanian age, is problematic. There may
be some kind of allocyclic signature in the Robledo sections, but autocyclic drivers clearly were important forces
in the local Early Permian sedimentary history. The red-bed fossil assemblages in the PTNM were early fit into
a rather simple model of intertidal flat depositional environments, but studies here indicate much greater depositional
complexity, and identify what are likely a mosaic of local paleonenvironments and taphonomic settings in
which the trace fossils and red-bed plant assemblages accumulated. The Early Permian geological record indicates
episodically increasing seasonality and climatic dryness around the equatorial regions of central and western
Pangea, a trend that began in the late Middle Pennsylvanian. During this period of warming, terrestrial floras
became increasingly heterogeneous spatially, and the Robledo paleofloras fit that pattern. Precise and extensive
age data for the Hueco Group section based on non-fusulinid and fusulinid foraminiferans indicate that the base
of the Leonardian (Artinskian) is very close to the base of the Robledo Mountains Formation. This means the
upper part of the local Hueco section is Leonardian, not Wolfcampian as long supposed.

The cauline and leaf cushion morphology of five species of anatomically preserved Lepidodendron are described from Lower and Middle Pennsylvanian coals of Euramerica. These species are Lepidodendron vasculare Binney, L. scleroticum Pannel, L. dicentricum C. Felix emend. DIMichele, L. serratum C. Felix emend. Leisman & Rivers, and L. phillipsii sp. nov. Lepidodendron brevifolium Williamson and Lepidodendron hickii Watson have morphologies distinct from other species of Lepidodendron and from each other. Their inclusion within the generic concept of Lepidodendron has been the major factor in the problems regarding separation of anatomically preserved Lepidodendron and Lepidophloios.
    The species of Lepidodendron comprise three distinct morphological groups with different patterns of reproduction and evolution. Lepidodendron vasculare, L. scleroticum, and L. phillipsii are similar anatomically. All were 8-20 m tall and bore deciduous lateral branches on excurrent trunks. Cones of the Achlamydocarpon varius-type were produced subterminally on the deciduous branches conferring plants with the capacity for low-level but sustained reproduction. Lepidodendron dicentricum trees were 10-15 m tall with synchronously determinate crowns. Achlamydocarpon varius-type cones were produced in large numbers near branch tips late in determinate growth - the trees were possibly monocarpic. Lepidodendron serratum was herbaceous and produced Achlamydocarpon takhtajanii-type cones. All species have non-coronate steles, ranging from haplostelic to siphonostelic in the large stems, a three zoned cortex with varying degrees of "dictyoxylon' development in the thick outer zone, and, except for L. serratum, a distinctly bifacial periderm with phelloderm consisting of alternating bands of thick and thin-walled cells and a homogeneous phellem.
    The morphological similarities of Lepidodendron vascalare, L. scleroticum and L. phillipsll suggest a close evolutionary relationship. Lepidodendron vasculare occurred in many different types of coal-swamp environments from the Westphalian A to the early Westphalian D. In the early Westphalian D, L. scleroticum and L. phillipsli first appeared in the same swamp floras as L. vasculare. This was followed by segregation of each species to a distinctive swamp depositional setting and flora, with little or no further cooccurrence. Lepidodendron dicentricum may have evolved from populations of L. vasculare, or a morphologically similar species, in the Westphalian B; L. dicentricum occurred in coal swamps up to the late Westphalian D. More morphological variability is displayed by L. dicentricum than by other species of coal-swamp lycopod trees, and each morpho-type is confined to a distinct type of coal-swamp environment. Lepidodendron serratum displays little morphological variability throughout its range in coal swamps, from the Westphalian A to the Westphalian D. Its evolutionary relationship to other species of Lepidodendron is not clear.
    Coal swamp environments may have been evolutionary refugia for Lepidodendron and Lepidophloios. Their inherent morphological conservatism, plus their highly specialized reproductive biologies, made these lycopods extremely well adapted to the aquatic conditions of the swamp. Major speciation probably occurred in extra-coal swamp environments, particularly in the case of Lepidodendron.

The anatomy and morphology of the stem of Lepidodendron dicentricum C. Felix are re-evaluated and re-interpreted on the
basis of specimens from eight coals in the United States. These coals extend stratigraphically from the Buffaloville (Indiana) equivalent coal, Cherokee Group of Iowa to the Baker Coal Member, Lisman Formation of western Kentucky. The species has not been reported previously from coals other than the Fleming Coal Member of Kansas, due primarily to the peculiar characteristics of the type specimens from that coal. The most apparent and superficial difference between these specimens and specimens from other coals isthe lack of secretory cells in tissues of Fleming Coal Member specimens; secretory cells are abundant in specimens from most other coals. In Fleming Coal Member specimens varying percentages of parenchyma cells internal to the elongate metaxylem tracheids have
secondary wall thickenings; this zone is re-interpreted as a pith rather than the inner zone of a two zoned protostele. Parichnos is
shown not to connect to the lateral groove beneath the leaf scar on the cushion surface as originally described. Large specimens of
L. dicentricum have anatomy that corresponds to that of Lepidodendron schizostelicum Arnold, also described originally from the Fleming Coal Member. L, schizostelicum is placed in synonymy with t. dicentricum.
  Several important characteristics of Lepidodendron dicentricum sepatate it from other species of Lepidodendron. Pith and primary
xylem are sharply delimited; in large specimens the primary xylem is divided into discrete units by longitudinal columns of
parenchyma that are continuous with broad wood rays; leaf traces are ensheathed by inner cortical cells throughout their length in the middle cortex; the outer cortex consists of homogeneous thinner-walled cells rather than alternating areas of thick and thin-walled cells; the periderm originated from a bifacial cambium, which produced histologically distinct phellem and phelloderm; there are conspicuous zones of secondary, tangential cell expansion between the leaf bases that correspond to interareas seen in compressions. Protostelic lateral branches, which may be cone peduncles, are borne subterminally on siphonostelic branches that usually lack wood. The
distribution of L. dicentricum correlates closely with that of Achlamydocarpon varius, which may represent the fructification of the plant. The habit of L. dicentricum is incompletely known; it did branch by anisotomous dichotomies at irregular intervals and of different angles. It appears to have been of greater height and more highly branched than Lepidophloios. An emended diagnosis of Lepidodendron dicentricum is given.

Carboniferous coal-forming swamps are an excellent system in which to evaluate the
effects of regional to global climatic changes on ecosystem structure and dynamics.
Stressful physical conditions restrict the access of most species, creating semiclosed
conditions in which the signal-to-noise ratio should be high. We examine patterns of
change in coal-swamp systems during the Pennsylvanian at three levels: landscapes,
habitats within landscapes, and species within habitats. The timing and extent of turnover
at these three levels suggest a hierarchial organization, in the sense that patterns at one
level emerge from interactions among elements at a lower level, and can have subsequent
reciprocal effects on the dynamics at that lower level.
Changes in the species composition of coals, and in the dominance-diversity structure
they define, occur continuously throughout the Pennsylvanian. However, there are distinct
breakpoints that allow us to recognize five basic organizational themes. Bach of these
breakpoints corresponds to an independently inferred change in regional or global climate.
Examination of species-level turnover patterns reveals highest values at the landscapelevel
breakpoints, suggesting at rust that climate change may be affecting species turnover,
which then scales upward directly into landscape changes. Estimation of the
relationship between species turnover and habitat patterns, however, suggests an intermediate
level of organization. Species turnover throughout the Westphalian occurs mostly
within habitats and on strongly ecomorphic themes; species of the same or closely related
and morphologically similar genera tend to replicate each other through time. It is the
proportion of habitats that changes at the landscape-breakpoint boundaries, and habitats
contain the ecomorphic elements that give the landscape its apparent dominance-diversity
structure.
At the Westphalian-Stephanian boundary, high levels of extinction eliminated sufficient
numbers of species that Westphalian ecomorphic patterns were destroyed and a new set of species-habitat dynamics was established. In combination with replacement patterns
during the Westphalian, the extinction suggests that biotic interactions among species
assist in creating a "fabric" or multiniche system that helps constrain the ecomorphic nature
of species replacements, whether such replacements occur through evolution within or
migration into the system. Loss or decline of a species creates a vacant niche, whose limits
are partially defined by the remaining biota. Major disruption of this system by extrinsically
induced extinction permits the system to reestablish the interaction fabric based on
the biologies of the new suite of species.

The cauline and leaf cushion morphology of Lepidophloios trees from lower and middle Pennsylvanian, American coal swamps
are described and compared with other Carboniferous specimens. More than one hundred specimens were anatomically studied from twenty-six localities in ten coals extending stratigraphically from the Magoffin Member, Breathitt Formation, Pottsville Group in the Appalachian Coal Province to the "Baker" Coal Member, Lisman Formation in the upper Desmoinesian Series of the midcominent Interior Coal Provinces. With few exceptions the stems are referable to one species along this entire stratigraphic range. The two previously described American species of Lepidophloios, L. kansanus (C. FELIX) EGGERT and L. pachydermatikos ANDREW & MURDY are placed in synonymy with Lepidophloios hallii (EVERS) comb. nov. which was originally described as a species of Lepidodendron. An emended diagnosis of Lepidophloios hallii is given and two taxa based on partially preserved specimens without leaf cushions are transferred from Lepidodendron to Lepidophloios as L. wilsonii (ANDREWS & BAXTER) comb. nov. and L. johnsonii (ARNOLD) comb. nov. on the basis of their cauline anatomy.
          The mature tree of Lepidophloios hallii attained a height of 10-20 m. A reconstruction of the crown suggests upright, compact, infrequent isotomous branching consistent with the lack of secondary supportive tissues in the branches. Most of the crown support was derived from the thick outer cortex. Cones were borne laterally in the upper crown and / or terminally on ultimate divisions of the crown. Specimens attributed to Lepidophloios kansanus are from the main trunk and lower part of the crown; those described as Lepidophloios pachydermatikos represent the middle and upper crown. There is no secondary xylem and very little periderm in these crown branches. Transitions between the two have been established and provide further documentation of positional differences in the tree of pith zonation, stelar dimensions, presence or absence of secondary growth and lateral branches, and depth of periderm initiation. Periderm development in Lepidophloios hallii originated from a bifacial phellogen. The size and degree of imbrication of leaf cushions are related to total size of the primary body and position on the cauline systems, hence to vegetative determinate growth. There is no evidence of continued leaf cushion expansion concomitant with secondary development of the stem. Leaf cushion morphology and their cuticles are very similar to those of Lepidophloios laricinus STERNBERG which is based on compressions and impressions.
          The most similar anatomically preserved European species to Lepidophloios hallii are L. harcoztrtii (WITHAM) SEWARD & HILL
and L. fuliginosus (WiLLIAMSON) SEWARD. All of these Upper Carboniferous species differ anatomically and morphologically
from the European Lepidophloios Wuenchianus (CARRUTHERS) SEWARD & HILL and L. scottii GORDON, primar ily from the Lower Carboniferous, and from the American L. johnsonii from the lower Pennsylvanian. These two groups of species, L. harcourtii and L. wuenchianus, overlap stratigraphically in the Namurian and Westphalian A. The L. w uenchiantts group is not known from coal swamp environments. The L. harcourtii group constitutes a major vegetationa! component of Euramerican coal swamps, with L. hallii stratigraphicall y complementing L. harcourtii and L. fuliginosus prior to and during the middle Pennsylvanian (Desmoinsian Series or U.S.G.S. interval C).

As vegetation evolved during the Palaeozoic Era, terrestrial landscapes were substantially transformed,
especially during the 120 million year interval from the Devonian through the Carboniferous. Early
Palaeozoic river systems were of sheet-braided style – broad, shallow, sandbed rivers with non-cohesive
and readily eroded banks. Under the influence of evolving roots and trees that stabilised banks and added
large woody debris to channels, a range of new fluvial planform and architectural styles came to
prominence, including channelled- and island-braided systems, meandering and anabranching systems,
and stable muddy floodplains. River systems co-evolved with plants and animals, generating new
ecospace that we infer would have promoted biological evolution. By the end of the Carboniferous, most
landforms characteristic of modern fluvial systems were in existence.

In this essay we examine the fossil record of land plants, focusing on the late Paleozoic. We explore the nature of this record in terms of what is preserved, where, why and with what biases. And as a consequence, how it can be used to answer questions posed at various spatial and temporal scales, what cautions we must consider when interpreting it, and what surprises it may hold. Generally speaking, the record of terrestrial plants is rich and reveals clear directional trends in phenotypic complexity, biodiversity, and ecosystem organization. It also has reasonably well understood taphonomic biases. It must be used with considerable caution, however, when researching time and location of evolutionary innovations and the development of ecological structure and interactions.

Fossil plants have been collected and described from strata near the Pennsylvanian-Permian boundary in three
areas of San Juan County, Utah. Collections made near Indian Creek east of Canyonlands National Park comprise
mainly tree fern foliage and sphenopsids from one stratigraphic level, and large logs of conifers with rare conifer
foliage from a higher level. A site on Lime Ridge west of Bluff, Utah, yielded abundant large branches of walchian
conifers together with calamitaleans and cordaitalean foliage. Sites in Valley of the Gods State Park, west of Lime
Ridge, produced mainly stems, with variable occurrences of foliage. Most of the stems are calamitalean or the
large tree fern Caulopteris, but a single medullosan pteridosperm specimen also was found, as were several small
fragments of the lycopsid Sigillaria. Tree fern foliage, Pecopteris, rare neuropterid foliage, and fragments of leafbearing
conifer branches also were identified. Thus, our collections contain a mixture of plants adapted to seasonally
dry conditions (conifers and possibly cordaitaleans) and those requiring wet substrates (calamitaleans, tree
ferns, lycopsids and pteridosperms). Red beds, dune sands, loess, and gypsum indicate aridity, on average, but with
intervals of more humid conditions. The combination implies an arid eolian depositional system traversed at times
by streams sourced on the Uncompahgre highland.