Chromosome Numbers in Compositae from the Southwestern United States

Abstract

Chromosome numbers are reported for 63 taxa of Compositae from the southwestern United States. Seventeen taxa are recorded for the first time, in- cluding a first report for the genus Enceliopsis (n=18). The chromosome numbers in this paper were compiled from ma- terial collected over a period of four years in the southwestern United States. Seventy counts are reported of which 17 are initial reports, in- cluding one new generic record. Three counts are new numbers for previously reported species. The remainder are largely of taxa in which there have been few reports. METHODS AND MATERIALS.-Chromosome numbers were obtained from meiotic and mitotic cells. For the meiotic counts, flower buds were fixed in Carnoy's solution (4 parts chloroform: 3 parts absolute alcohol: 1 part glacial acetic acid) and stored under refrigeration until examined. The anthers were squashed in aceto- carmine by the technique of Turner and Johnston (1961). Pollen mother cells were examined for chromosomes at diakinesis or metaphase I. Seeds for mitotic counts were germinated on moist filter paper. The emerging root tips were placed in a saturated solution of paradichlorobenzene for 1-4 hours, then squashed in 2% aceto-orcein. The mitotic counts are denoted in table 1 by asterisks