ISOLATION OF A DIPLOID, APOMICTIC PLANT OF HIERACIUM-AURANTIACUM

As in most taxa that contain gametophytic apomicts, all of the apomict ic biotypes studied so far in the genus Hieracium subgenus Pilosella h ave been recorded as polyploids. As: part of a study of variation in a pomictically derived populations of H. aurantiacum, a diploid plant wa s identified, Apospory, the mechanism of apomixis typically observed i n this taxon, was observed in this plant. Unreduced megagametophytes t it various developmental stages were commonly observed in the developi ng ovules, and endosperm formation was autonomous. The eventual seed s et, however, was low. This appears to have been due to the proliferati on of competing megagametophytes and embryos within each ovule. Pollen sterility was also observed, primarily resulting from the dysfunction of microgametogenesis at tile uninucleate stage.