A phylogeny of Packera (Senecioneae; Asteraceae) based on internal transcribed spacer region sequence data and a broad sampling of outgroups

A phylogeny of Packera is presented based on sequence data from the interna l transcribed spacer region of nuclear ribosomal DNA of 26 species (28 popu lations) of Packera and 23 outgroup taxa, including representatives of all three subtribes of the Senecioneae. The results support a Mexican origin fo r Packera, with its closest relatives found among Old World taxa in the sub tribe Senecioninae, such as Senecio jacobaea and Pericallis. Packera specie s from the west coast of the United States, previously included in the sect ion Bolanderi of Greenman, are part of a basal assemblage including species of Greenman's Mexican section Sanguisorboidei. The rest of Packera separat es into two sister groups, one containing species from the Arizona-New Mexi co region and the other containing more geographically diverse taxa. Among the outgroups, New World Senecio species are monophyletic and two Tussilagi noid assemblages are strongly supported; the Tephroseroid group (Tephroseri s and Sinosenecio) plus Petasites combine with the Luina complex to form a clade of north temperate taxa, and the four Mexican genera (Psacalium, Robi nsonecio, Barkleyanthus, and Pittocaulon) form a monophyletic group. (C) 20 00 Academic Press.