Some aspects of the phytogeography of Carex

Abstract

The worldwide distribution of Carex suggests that it originated in the early Tertiary. The genus reaches its greatest diversity in the temperate regions of the world. Except for SE Asia, it is generally absent from lowland tropical areas and is especially rare in Africa. Subgenus Indocarex, although abundant in SE Asia, also occurs in east Africa, the Mediterranean region, and tropical America. Such a distribution is consistent with the view that the subgenus originated in the early Tertiary, adjacent to the Tethys seaway. The genus contains a variety of species or species groups that exhibit disjunct distribution patterns such as bipolar, amphiatlantic, and eastern Asia – eastern North America distributions. The evidence in most of these examples favours a relatively late origin for these distributions. A number of sections contain species complexes in which several closely similar species are sympatric and show little ecological differentiation. At the moment we have no satisfactory explanation of the processes of speciation and migration that led to this situation.