DiMichele, W. A. (Department of Paleobiology, NMNH, Smithsonian Institution, Washington, DC 20560), T. L. Phillips (Department of Plant Biology, University of Illinois, Urbana, IL 61801), and H. W. Pfefferkorn (Department of Earth and Environmental Science, University of Pennsylvania, Philadelphia, PA 19106). Paleoecology of Late Paleozoic pteridosperms from tropical Euramerica. J. Torrey Bot. Soc. 133: 83–118. 2006.— Late Paleozoic pteridosperms are a paraphyletic group of seed plants that were prominent elements of tropical ecosystems, primarily those of wetlands or the wetter portions of seasonally dry environments. Because the group is more a tradition-based, historical construct than a well circumscribed phylogenetic lineage, the wide variance in ecological roles and ecomorphological attributes should not be surprising. Pteridosperms can be the dominant canopy trees in local habitats, prominent understory trees, scrambling ground cover, thicket-formers, or liana-like plants and vines. Some species appear to have been weedy opportunists, although this ecological strategy seems to be a minor part of the wide spectrum of pteridosperm life habits. Most pteridosperms appear to have preferred wetter parts of the landscape, though not standing water, and relatively nutrient-rich settings (in comparison with groups such as tree ferns or lycopsids). Of the Paleozoic pteridosperms as traditionally circumscribed, only the peltasperms survived to become major elements in the Mesozoic. However, these plants may have been part of a derived seed-plant clade that also includes the corystosperms and cycads (see Hilton and Bateman, this volume), indicating that only the most derived of the Paleozoic pteridosperm lineages, those that appear to have evolved initially in extrabasinal settings, persisted into the Mesozoic.