GEOGRAPHIC DIFFERENTIATION IN ATRIPLEX CONFERTIFOLIA

Atriplexconfertifolia (Chenopodiaceae) consists of ploidy races extending from diploid through decaploid and is dissected into many racial groups by cytological and flavonoid relationships. On the basis of morphology, the species can be divided into two major subdivisions, one centered in western Nevada and inhabiting chiefly the Great Basin, and one centered in the Colorado Plateau. Western Nevada plants are distinguished by smaller and narrower leaves, as well as by darker spines and other charactristics. Because western Nevada is situated in the lee of the Sierra Nevada Range, it received reduced amounts of rainfall during Pleistocene and Holocene times. These reduced leaf dimensions of A. confertifolia of the rain shadow zone may thus reflect an evolutionary response to aridity.