Aim: Separation of regeneration niches may promote coexistence among closely related plant species, but there is little evidence that regeneration traits affect species ranges at large geographic scales. Here we address patterns of co-occurrence within the genus Selaginella, an ancient lineage of free-sporing, heterosporous, vascular plants. Specifically, we ask whether differences between species in spore size are associated with the extent of overlap in their geographic ranges, a measure of opportunity for ecological interaction. Taxon:...