HETEROPLOIDY IN SEDUM ROSEA (L.) SCOP.

Cytotaxonomists have found manv different chromosome numbers in the 'Crassulaceae. In several cases differences in chromosomes have provided valuable information concerning relationships within the family (d. Baldwin. 1939: Uhl, 19-18). Such criteria of relationship must be used with some caution, however, for in a growing number of instances heterop~oi~ly has been found in morphologically similar plants. Eupolyploidy has been the commonest type of heteroploidy detected (d. Baldwin, 1939, 1943), hut there are also several cases of apparently intraspecific aneuploidy. S cdum rose;, (L.) Scop. provides one of these. Scduui rosca. as conceived by Berger (1930) and many other recent taxonomists. is a highly polymorphic, usuallv dioecious species that is widelv distril;uted in the northern parts of North America and Eurasia. The taxonomv and synonymy are rather complicated, and distinct binomial combinations have been proposed by a number of authors for forms that other taxonomists include in the one species. Because of its dioecious. tetramerous flowers, Linnaeus kept the species apart from Scduni and created for it the genus Rliodiola. A number of modern taxonomists still recognize Rhodiola as a genus, but most recent students of Scduui (e.g., Praeger, 1921; Berger, 1930; Froderstrom, 1930). are agreed that it is best subordinated to SeduIII , possibly as a section (Berger). The latter treatment is followed here. Previous workers have studied collections of Seduni rosea from Greenland through Europe and Asia to Japan. In all cases they have found gametic chromosome numbers of 11 or somatic num-