Evidence from cytology presented here and also the evidence obtained from many artificially produced hybrids indicates that the mostly large and thick-leaved species with lateral inflorescences, or at least most of them, form a natural group, referred to here as sect.
Seduni rosea is a highly polymorphic, usuallv dioecious species that is widelv distril;uted in the northern parts of North America and Eurasia and is best subordinated to SeduIII , possibly as a section (Berger).
Rough measurements of nuclear volume support the conclusion that members of two species complexes differ in the types of chromosome change predominating in their evolution, polyploidy in S. Aizoon and structural chromosomal rearrangements inS.
The chromosomes of probably all known species of Graptopetalum and Thompsonella and of two artificial hybrids are reported, with a discussion of the very high chromosome numbers found in two species.
Study of hybrids of these two species with numerous others leads to the conclusion that each of the two is effectively diploid, with a genome consisting of 33 chromosomes that are all different and that do not pair with each other.
Polyploids are autopolyploids and any different alleles of their multiple genes can be shuffled freely at meiosis and reapportioned in any combination, which allows them to undergo rapid rates of genetic recombination, thereby greatly increasing chances of adapting to rapid changes in geology and climate of the Andes during the Pliocene and Pleistocene.