The cytology of Brachycome. I. The subgenus Eubrachycome: A general survey

Abstract

Chromosome number determinations and cytological observations are reported for 37 recognized taxonomic species and varieties, and for a number of undescribed species and chromosome races in Eubrachycome. Additionally, chromosome numbers are reported for six species of Metabrachycome and two species of related genera. A wide range of numbers has been found. It is inferred that x = 9 is the primitive base number in the group.

Eubrachycome has used various modes of chromosomal change, including polyploidy, amphidiploidy, decrease in base number, and the establishment of B. chromosomes. The present taxonomy of the group requires revision, taking into account cytological data.

Primitive Eubrachycome was probably a mesic perennial. The evolution of desert species has involved reduction in chromosome number and the adoption of the annual habit, but other methods of desert adaptation have been available. Many species are chromosomally unstable, and may have been subject to catastrophic selection.