Cytotaxonomy and cytogeography of the goldenaster genus Heterotheca (Asteraceae: Astereae)This paper is one of a selection of papers published in the Special Issue on Systematics Research.

Abstract

Between 1948 and 2008, 668 chromosome number determinations have been reported for individuals of the goldenaster genus Heterotheca Cass. (Asteraceae: Astereae) from Canada, Mexico, and the United States, including 285 newly reported here. This common group of mostly western North American herbaceous annuals and perennials is subdivided into three sections, the most complex of which is section Phyllotheca . Differences of opinion about the taxonomy of the goldenasters, numerous synonyms, and the lack of a comprehensive treatment of the polymorphic villosa complex and other species complexes in section Phyllotheca made it difficult to organize the data into a meaningful discussion of the cytotaxonomy and cytogeography of this genus. Here I present the geographic distribution of all published counts and cytogeography maps of all species of Heterotheca, assigning taxa following recent taxonomic revisions. The sample sizes for species sampled ranged from 1 to 228 reports. All species have a base number of x = 9. Only diploids (2n = 9II or 2n = 18) were found in Heterotheca oregona (Nutt.) Shinners (the single species of sect. Ammodia ) and in the three species of section Heterotheca. Both diploids and (or) tetraploids were found across 18 sampled species of section Phyllotheca, with the frequency varying among them; nine species are known only at one ploidy level (either diploid or tetraploid; three species each). Only four triploids (2n = 9III or 2n = 27) were encountered in section Phyllotheca; two were putative interspecific hybrids. One new nomenclatural combination is proposed: Heterotheca inuloides var. leptoglossa .