Any form of * asexual reproduction , including vegetative propagation. The term is very often used in a narrower sense to mean the production of seeds without fertilization occurring. In this restricted sense the term is synonymous with agamospermy. Seed production by apomixis may occur either by the formation of a diploid embryo (see adventive embryony ) or embryo sac by a somatic cell, or by suppression or modification of the meiotic process to give unreduced megaspores (see diplospory , aneuspory ). Development into a mature diploid embryo can then proceed without fertilization (see parthenogenesis , pseudogamy ). Apomixis is usually associated with polyploidy. An organism that reproduces by apomixis is termed an apomict. Facultative apomicts, e.g. the cinquefoils (Potentilla), can reproduce both sexually and apomictically. In such species the incidence of apomixis may be affected by environmental factors, such as photoperiod. Obligate apomicts can only reproduce apomictically. Often these are triploids or pentaploids that cannot produce viable pollen. Plants that form apomictic complexes are notoriously difficult to classify. Some apomictic races are so constant that they have been given taxonomic status as species (for example, almost 400 species of Rubus have been recognized in Britain). |
