Generic Relationships in Gochnatioideae (Asteraceae) Including Tehuasca, a New Genus from Northeastern Mexico.

Abstract

Phylogenetic analysis of the Internal and External Transcribed Spacer regions of nuclear ribosomal DNA was used to elucidate the taxonomic limits of the genus Gochnatia and generic relationships in Gochnatioideae. These analyses place Richterago and Cnicothamnus sister to Gochnatia and collectively sister to the discoid genera Anastraphia and Nahuatlea. Gochnatia is monophyletic and has three main clades each corresponding to formal sections of the genus, namely Gochnatia, Moquiniastrum, and Pentaphorus. The recently described genus Nahuatlea was not monophyletic with its species found in a grade of three clades and only one species sister to the Caribbean genus Anastraphia. Nahuatlea magna is sister to Anastraphia and a new genus, Tehuasca, is erected with this species as its type. Tehuasca shares with Anastraphia corollas with glandular trichomes but differs from Anastraphia in having white to yellow corollas, recurved lobes of the corollas and leaf margins without spiny mucros. Tehuasca magna is a native species of northeastern Mexico.