Many species of the Fossombroniineae are adventives, occurring most abundantly in either disturbed or seasonally dry habitats. Their distribution within communities is generally patchy, with the patches isolated from each other by denuded soil or more often by other vegetation. Frequently, all patches of the community are comprised of but a single species, but in some localities several species may coexist. To investigate the spatial relationships among species as well as infraspecific patch dynamics and establishment potential, field studies were undertaken at Bastrop State Park near Austin, TX. In year one of the study, patch distributions of Fossombronia and Petalophyllum were mapped in eight randomly selected sites within the park in the early spring growing season. To evaluate microhabitat variation among these sites, soil pH, temperature at patch surface, and intensity of red, far-red and blue radiation were measured. Soil samples were systematically removed from each site for subsequent spore bank analysis to assess the re-establishment potential of each species. The eight sites were revisited and sampled for spore bank analysis in midsummer of the following year to evaluate the impact of seasonal changes on community structure. These studies suggest that patches of the four taxa found within the sites are clustered by species rather than being randomly mixed, with typically no more than three species at any one site. In year one, only F. foveolata and a few patches of Petalophyllum germinated from the spore bank soil samples, while in year two, a single patch of F. porphyrorhiza also developed. Such germination events modify patch distributions but species composition of each site seems to be consistent from year to year.

Key words: community mapping, establishment dynamics, Fossombroniineae, population structure