Cytogenetic studies in the genus Atriplex (Chenopodiaceae)

This work examined the karyotypes of 55 Atriplex species including 24 annua l and 31 perennial taxa. The basic chromosome number was x=9 for all specie s. The annual Atriplex consisted 19 diploid (2n=9x=18), four tetraploid (2n =4x=36), and one hexaploid (2n=6x=54) species whereas, the perennial taxa i ncluded 20 diploids, ten tetraploids, and one hexaploid. Comparisons on chr omosome morphologies revealed that while annual species were highly variabl e in their karyotype constitution, the perennial Atriplex had relatively un iform chromosome patterns. Some annual species, such as A. subtilis (the mo st variable karyotype) and A. depressa exhibited remarkable differences in haploid chromosome length, suggesting variation for DNA content. Karyotype analysis suggested that perennial species have evolved predominantly by cen tromeric shifts and polyploidy while the annual Atriplex differed by additi on and deletion of chromatin associated with structural chromosome changes and polyploidy.