ABSTRACT
In sexual plants, prolonged resting stage of the egg cell is desirable to secure fertilization. Polyploidy may be thought to eliminate this long resting stage, which would be useful in an apomict. Gametophytic apomixis is inseparably connected both with polyploidy and hybridization. Polyploidy, or the avoidance of meiotic reduction, may induce physiological or developmental changes resulting in parthenogenetic initiation of embryos. The chapter refers to the "diploid-tetraploid-dihaploid cycles" where changes in level of ploidy are combined with changes of mode of reproduction. Newly formed dihaploids are often sexual, usually weak, and more or less sterile. Even if self-fertilization occurs in facultative apomicts, they are polyploid, with multisomic inheritance, which retards reduction of heterozygosity through inbreeding. In Limonium, sexual taxa have a dimorphic incompatibility system in connection with heterostyly. Gametophytic apomixis and self-fertilization seem mutually exclusive, and apomixis has not been expected in taxa with floral adaptations that promote self-fertilization.
