Article

Various evolutionary pathways involving hybridity are discussed, with examples taken from Viola sect. Melanium. Karyotype analysis will often enable reconstruction of parentage of hybridogenous polyploids. The study of hybrid populations shows that hybridity, including backcrosses, is a frequent phenomenon, and that mechanisms exist to baI ance karyotypes with uneven numbers of chromosomes, thus circumventing sterility. Karyotypes in this group have often evolved by (mostly descending) aneuploidy from a postulated originaI basis of x = 11 chromosomes, leading down to the level x = 2 (first reported here) which equals the lowermost number known so far in plants.