Cytologically the family Crassulaceae is probably the most diverse group of angiosperms. Chromosome numbers range from 2n = 8 to In = 640, and basic numbers from x = 4 to x = 37 and more. The genus Sedum especially is extremely variable. The 54 European species for instance, comprise about 140 different cytotypes. Chromosomes of Crassulaceae are generally very small, usually less than 2 pm, but variation in chromosome size is nevertheless considerable. Chromosome length may vary 10-fold among species as well as among chromosomes of a single karyotype. The amount of DNA per nucleus is proportional to chromosome number and chromosome length. Although 2C values are extremely low in many species (0-5 pg and less), 40-fold differences have been observed among species.