Chromosomes of Villadia and Altamiranoa (Crassulaceae)

Villadia, ranging from Texas to Peru with some 25 species, has a rather dis tinctive thyrsoid to spicate inflorescence, and we keep it as a genus separ ate from Sedum. Twenty species show every gametic chromosome number from 9 to 17 and also 20-22 and higher Chromosome pairing in hybrids shows that th e species differ by many translocations and that species with 21 or lower a re effectively diploid. More specialized species tend to have fewer and lar ger chromosomes, suggesting that through time translocations have rearrange d the ancestral genome into fewer units. We suspect that relocated genes ma y be: programmed differently, affecting phenotype. Thus Villadia is like Ec heveria in having a remarkably long descending series of evidently diploid chromosome numbers. Altamiranoa, often included in Villadia, with about 15 species from Mexico south, more closely resembles Sedum in its broadly cymo se inflorescence. It appears polyphyletic, with no clear boundary from Sedu m, and we disperse its species in Sedum. The ten species studied have gamet ic numbers from 20 to 29 that probably are effectively diploid, with a few higher and probably polyploid. Again, chromosome pairing in hybrids shows t hat the species differ by many translocations. Putative relatives in Sedum section LEPTOSEDUM have n = 26 to 31. Thus cytologically as well as morphol ogically Altamiranoa has remained more similar than Villadia to its Sedum r elatives.