Chromosome Counts of Compositae From the United States, Mexico, and Guatemala

Abstract

Chromosome numbers can be extremely useful in systematic studies, particularly for helping to reveal evolutionary relationships. For the past fifteen year numerous chromosome reports from plants have been published, especially in the Compositae, and these counts have been compiled in several major sources (Darlington & Wylie, 1955; Cave, 1958-65; Ornduff, 1967-69; Fedorov, 1969; Moore, 1970-72). However, a rapid glance through these references indicates not only that many species never have been counted, but also that many taxa are known only from a single plant in one population. In view of the common occurrence of euploid and aneuploid races in plants as illustrated by several detailed investigations (e.g., Lewis, 1962, 1970; Stuessy, 1971a), it is desirable to have several to many counts from each species before accurate judgments can be made regarding evolutionary relationships (Stuessy, 1971b; Kovanda, 1972; Strother, 1972). The present paper helped to remedy these deficiencies int he Compositae by : (1) reporting first chromosome counts for several genera, species, and varieties; and (2) reporting additional populational chromosome counts for taxa documented previously