Thelesperma subnudum is a herbaceous, perennial composite found in the mountain west region of the United States. Thelesperma subnudum is part of a species complex which includes four other taxa; T. marginatum, T. subnudum var. alpinum, T. caespitosum, and T. pubescens. Thelesperma marginatum and T. caespitosum have been classified as varieties of T. subnudum by various authors. Thelesperma caespitosum, T. pubescens and T. subnudum var. alpinum are extremely rare and potentially endangered. Critical to their survival and proper management is a better understanding of the relationships within this complex. Morphological, ecological and molecular characters were examined for this study. Morphological and ecological information was gathered from herbarium specimens and labels, and from field observations. Thelesperma caespitosum, T. pubescens and T. subnudum var. alpinum all shared a shorter, denser, mound-forming habit and grew at higher elevations than T. marginatum or T. subnudum. Whereas, T. subnudum and T. marginatum were glabrous and formed taproots, a thick, branched caudex and various amounts of pubescence were indicative of the three rare taxa. An enzyme electrophoretic survey was also performed using starch gels. Data from the allozyme banding patterns of 23 populations were compiled and used in a phylogenetic analysis based on parsimony. The phylogenetic analysis indicated that T. subnudum var. alpinum was more closely related to the T. pubescens/T. caespitosum clade than to T. subnudum. Thelesperma marginatum and T. subnudum are most likely distinct species based on their allozyme divergence and allopatric distributions. With the congruence found among our data sets elevation of T. subnudum var. alpinum and retention of T. caespitosum as distinct species may be warranted.

Key words: allozymes, Asteraceae, systematics, Thelesperma