PHYLOGENETIC RELATIONSHIPS OF THE MEXICAN TUSSILAGINOID GENERA (ASTERACEAE: SENECIONEAE)

摘要

The Mexican tussilaginoid genera (Asteraceae: Senecioneae) consists of 13 genera distributed from the USA to Panama, with most species occurring in montane regions from Central Mexico to Guatemala. Presently, 142 species are recognized in this clade,with many considered to be endemic to threatened pine-oak or cloud forest ecosystems. Endemism is abundant among the clades identified, with over half of the species restricted to relatively small geographic areas. Moreover, most members of the Mexican tussilaginoid inhabit montane regions at or above 1500 m in Mexico and Guatemala and are thus under immense pressure from human land use. We conducted a phylogenetic investigation of the Mexican tussilaginoid genera and outgroup taxa, using nuclear ribosomal DNA sequences of 74 species from 17 different genera. We also compared competing hypotheses regarding the monophyly of three genera that were supported as monophyletic in previous investigations using topology-based hypothesis testing. The results ofour analyses support thirteen clades within the Mexican tussilaginoid genera. Topology-based hypothesis testing indicated that the genera Pittocaulon, Psacaliopsis, and Roldana are not monophyletic. The genus Telanthophora, by contrast, was found monophyletic, but nested within Roldana.