Cytology of the highly polyploid disjunct species, Allium dregeanum (Alliaceae), and of some Eurasian relatives

Chromosome numbers are given for 16 taxa in Allium Section Allium, three in Section Codonoprasum, two in each of Sections Molium and Rhizirideum and one in each of Sections Kaloprasum, Megaloprason and Melanocrommyum. The basic chromosome number is x=8 in all except Section Molium, in which the studied species unusually have x=7. Polyploidy common in the genus, with over half of the studied taxa in Section Allium having polyploid representatives. The highest ploidy levels found so far in the genus occur in A. dregeanum (2n=8x=64 and 10x=80), which is counted here Tor the first time. Although highly polyploid, this disjunct South African species forms only bivalents during meiosis. The chiasmata are proximal, an uncommon phenomenon reported also in hexaploid A. ampeloprasum. Although A. dregeanum is genetically related to A. ampeloprasum, the suggestion that it is a cultivated variant of that species introduced to South Africa by the early settlers is unlikely. (C) 1997 The Linnean Society of London.