A Molecular Systematic Study and Taxonomic Revision of Psilactis (Asteraceae: Astereae)

Intergeneric and interspecific relationships of Psilactis were studied using data from restriction site analysis of chloroplast DNA and nuclear rDNA. Molecular evidence supports the removal of Psilactis from Machaeranthera and its alliance with Aster. Within the Aster lineage, chlo- roplast DNA data support an alliance composed of members of Psilactis that have n = 4 (P. tenuis, P. boltoniae) and those of Aster subg. Oxytripolium that are based on x = 5 (A. subulatus, A. tenuifolius), separating them from the n = 9 species of both Aster and Psilactis. Evidence from nuclear rDNA, in contrast, supports different alignments by combining n = 4 and n = 9 species of Psilactis and by allying the n = 5 and n = 10 species of Aster subg. Oxytripolium with other species of Aster. Comparison of cpDNA results with evidence from morphology, rDNA, and isozymes suggests that hybridization may account for some relationships supported by chloroplast DNA. Psilactis is re-established as a distinct genus of six species, with P. mexicana placed in synonymy under P. gentryi. The following new taxonomic combinations are made: Psilactis gentryi, Psilactis odysseus, and Psilactis hetero- carpa.