Eric Walther classified three generally epiphytic species in his series Spicatae of Echeveria. Two of these, E. rosea (n = 34) and E. pittieri (n = 62) are distinctive, but E. chiapensis is not distinguishable from E. rosea. Certain plants from Oaxaca and Veracruz closely resemble E. rosea vegetatively but differ in the form of their flowers, and they have n = 51 or 50 1. We describe them here as a new species, E. tencho. All three species hybridize readily with many other Mexican Crassulaceae in cultivation.
Although we first thought that E. rosea was a tetraploid and E. tencho a hexaploid having a common ancestor with n = 17, analysis of chromosome pairing in their hybrids with other species requires a different interpretation. At meiosis in its hybrids none of the 34 gametic chromosomes from E. rosea can synapse with any of its others, although many synapse with parts of one or more chromosomes from the other parent. They are all different, and, like many other Mexican Crassulaceae that have this many chromosomes, E. rosea is effectively diploid. The behaviour of the 50 or 51 chromosomes from E. tencho at meiosis in its hybrids suggests that it may be a diploidized descendant of autotetraploid ancestors with n = 50, which were in turn derived from diploids with n = 25. E. pittieri appears to be an allotetraploid, but its ancestors are not known. The species of Walther's series Spicatae appear to be much less closely related than the similarities in their appearance and habitat suggest.