PARALLEL EVOLUTION

Summary A considerable number of instances are discussed where parallel developments outside family relationships occur, restricted in geographical distribution: divaricate shrubs in New Zealand, with 51 species in 23 families, the Eucalypt leaf type in Australia, occurring in 12 families, terete and holly‐type leaves in Western Australia, red autumn leaf coloration in Northeastern America and Japan, leaf convergence in Mediterranean climates, the cushion plants in Southern Patagonia, parallels in anatomical structure in the Southwestern United States, red tubular hummingbird flowers of the Southwestern United States. This is contrasted with cases of convergent characters on the genus or family level, or geographically unrelated parallel development. In the discussion it is argued that such parallel development might well represent rare‐nonsexual transfer of chromosomal segments. It is obviously one of the major evolutionary mechanisms in the development of the multitude of dicotyledonous species.