A Classification of the New World Species of Aster (Asteraceae)

Abstract

In order effectively to list and comment on the results of cytological investigations inAster in a companion paper, a scheme of infrageneric classification is presented which utilizes the basic chromosome number as a pivotal diagnostic character. Reasons are stated as to why, with the exception ofUnamia Greene which is transferred toSolidago, and the commonly recognized generaLeucelene Greene,Machaeranthera Nees andXylorhiza Nutt., none of the segregate genera previously proposed or recorded in the literature is upheld. Instead, these taxa are being given subgeneric or sectional rank. Two additional subgenera are established to accommodate the species groups traditionally placed in “Aster proper,” which are characterized by having basic chromosome numbers ofx = 5 andx = 8, respectively. Altogether ten subgenera of the genusAster, five of them subdivided further into a total of 24 sections, are recognized as having representative species in the New World. All basionyms and type species are listed, and a number of new combinations and status changes are validated in accordance with the International Rules of Botanical Nomenclature. Where known (from literature and personal research), chromosome numbers are recorded for the species.