Comparative ecology and life-history biology of arborescent lycopsids in Late Carboniferous swamps of Euramerica

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. These include: determinate apical growth of the aerial shoot system and the anchoring stigmarian system, which have marked homologies; limited amount of secondary xylem, lack of secondary phloem, and periderm as the major support tissue; differentiated gas-diffusion system associated with appendages, including lacunae and parichnos; abscission of appendages and lateral branches; retention of leaf cushions; and close relationships between mode and timing of branching, to cone-bearing and heterosporous reproductive biologies. Vegetative structure-functions explored include the possibility that lacunae and parichnos were involved in internal mediation of gas diffusion as opposed to aeration functions. The possibility exists that parts of the stigmarian system were involved in CO2acquisition from substrates; some may have been photosynthetic. These functions are considered in the context of the light sharing and diffuse photosynthesis evident in the pole architecture. The combination of such possibilities is related, in part, to the xeromorphic characteristics of the arborescent habit, raising the question about a modified kind of C3photosynthesis such as CAM (Crassulacean Acid Metabolism). Stigmarian lycopsids dominated tropical Westphalian coal swamps as an array of genera with relative distributional abundances reflecting habitat partitioning according to edaphic conditions, including temporal disturbance patterns. Species appear to exhibit different levels of tolerance to disturbances and range from colonizers to site occupiers. Paralycopodites, with prolific, free sporing, bisporangiate cones, was most abundant in frequently disturbed, partially exposed, peat- to mineral-rich habitats (ecotonal). Monosporangiate Lepidophloios and Lepidodendron were associated typically with deeper, standing-water habitats, and, in association with terminal branching, monocarpically produced specialized monosporic megasporangium-sporophyll units, termed aquacarps. Diaphorodendron species were monosporangiate with aquacarps and range from a