Apomixis - Kriton K. Hatzios
Apart from the occaisonal cross-pollination, heterozygosity may be maintained in many other ways. One of these is vegetative multiplication as in the case of Bermuda buttercup (Oxalis pes-carpe). Another way of "fixing" heterozygosity is by apomixis, where zygotes are formed without fetilization of the egg by the gamete from the pollen grain. This phenomenon is sometimes found in weeds; good examples being the dandelion (Taraxacum offiicinale) and perforate St. Johnswort (Hypericum perforatum).