The relationship between phylogenetic distance and ecological similarity is key to understanding mechanisms of community assembly, a central goal of ecology. The field of community phylogenetics uses phylogenetic information to infer mechanisms of community assembly; we explore, the underlying relationship between phylogenetic similarity and the niche. We combined a field experiment using 32 native plant species with a molecular phylogeny and found that closely related plant species shared similar germination and early survival niches. Species also competed more with close relatives than with distant relatives in field soils; however, in potting soil this pattern reversed, and close relatives might even have more mutalistic relationships than distant relatives in these soils. Our results suggest that niche conservatism (habitat filtering) and species interactions (competition or facilitation) structure community composition, that phylogenetic relationships influence the strength of species' interactions, and that conserved aspects of plant niches include soil attributes.