PHYLOGENY OF OPUNTIOIDEAE (CACTACEAE)

Opuntioideae are a diverse subfamily of Cactaceae with significant diversity of form and habitat and wide distribution throughout the New World. Nuclear ribosomal ITS and chloroplast trnL- trnF region DNA sequence -based phylogenetic analysis of Opuntioideae derived from Bayesian methods is presented. This analysis supports the following relationships: Opuntioideae are monophyletic; the subfamily is made up of four major lineages (Maihueniopsis-like species, Pterocactus, other terete-stemmed species, and flat-stemmed species). The two deepest lineages (including most species of Maihueniopsis and all Pterocactus) are marked by diminutive, succulent, often geophytic habit and are leafless at maturity. These analyses suggest that Opuntioideae have geographic origin in west-central South America. Generic circumscription is considered in the context of the recovered relationships. Maihueniopsis is recovered in multiple lineages. Many currently accepted genera may be para- or polyphyletic.