EUTRIPLOID FACULTATIVE AGAMOSPERMY IN TARAXACUM

SUMMARY Diploidy is reported in the species Taraxacum brachyglossum, T. subcyanolepis and in the T. punctatumlaustriacum complex. In each case, diploids are found in company with triploids of the same species, which are shown in the case of T. brachyglossum to be facultative agamosperms. These have regular pollen and show incomplete seed-set in the absence of cross-pollination. Triploids in T. subcyanolepis and T. punctatum/austriacum are similar and are also thought to be facultative agamosperms. This is the first report of eutriploid, facultative agamospermy in Taraxacum. Diploid sexuals may be recognized by regular pollen and no seed-set in insect-free conditions. Obligate agomosperms have highly irregular pollen, large regular pollen or no pollen and set good seed. It is shown that sexual diploids can give rise to triploids apparently as a result of fertilization by incompletely reduced pollen in triploids. Some triploids can give rise to diploids, perhaps through reduction in the female meiosis, which is synaptic, followed by fertilization with haploid pollen. Suggestions are made as to the mechanism controlling facultative agamospermy in disomic triploid and eutriploid individuals. Critical phases seem to be the course of the female meiosis and the timing of autonomous embryony.