Phylogenetic Relationships in <I>Echinocereus</I> (Cactaceae, Cactoideae)

Abstract

Echinocereus is the third most species-rich genus in the Cactaceae. It is distributed in North America from Mexico to the central U. S. A. Previous molecular phylogenetic studies have indicated that the genus is polyphyletic, but incomplete taxon sampling and unclear resolution have hindered the formal re-evaluation of generic and infrageneric circumscriptions. To address this problem, we analyzed six plastid regions (matK, rbcL, psbA-trnH, trnQ-rps16, rpl16, and trnL-F) using maximum parsimony and Bayesian inference criteria for 59 species, including all previously proposed infrageneric entities and representing the full range of morphological variation known in the genus. Our results support the monophyly of Echinocereus if E. pensilis is excluded and reestablished as the monotypic genus Morangaya. Two additional morphological characters, erumpent flower buds and green stigma lobes, further support the circumscription of Echinocereus sensu stricto. Phylogenetic analyses recovered nine main clades in Echinocereus s. s., one of which corresponds to the Triglochidiati section; the remaining clades did not correspond to any other recognized sections. We suggest a re-evaluation of previously proposed infrageneric entities.