Why are there so many Primitive Angiosperms in the Rain Forests of Asia-Australasia?

The rain forests of tropical and subtropical Asia-Australasia contain significantly greater concentrations of ‘primitive’ angiosperm families than do those either of the African continent or of the Neotropics. This concentration of primitive taxa has been interpreted as a reflection of their origin in this region, and has led evolutionary botanists to propose that angio-sperms actually evolved ‘somewhere between Assam and Fiji’ (Takhtajan, 1969). A presumed origin in Asia-Australasia has also been supported by the overlap in that area of many family or subfamily pairs, such as the ‘northern’ Magnoliaceae and the ‘southern’ Winteraceae, or ‘north-em’ Fagoideae and ‘southern’ Nothofagus. Current views based on the fossil record suggest that angiosperms initially radiated from Western Gondwana or SW Laurasia. This raises the question as to why so many primitive angiosperm families are currently concentrated in the area from NE Australia to southern China. The present paper tries to explain this anomaly by tracing the history of some primitive angiosperm families and some associated taxa by reference to the fossil record, and also in relation to the changing positions of tectonic plates, and changing global climates during the course of the Late Cretaceous and Tertiary. It is suggested that the concentrations of primitive angiosperms in this region are relict, and have nothing to do with angiosperm origins.