Species diversity and advancement of Swertia (Gentianaceae): Ecological and morphological correlates

Abstract

Swertia L. with about 150 species worldwide is one of the most divers genera of the Gentianaceae. Based on previous work for morphological phylogeny of the family, Swertia can be considered as a primitive genus of the temperate subtribe Gentianinae Gilg. To explain diversity in Swertia, species number per 100, 000 sq. km were calculated and mapped for important parts of the generic range, evolutionary advancement indices (AI) for 118 species were determined (based on morphological traits) and a correlation analysis, with ecological and phenotypical variables, was imdertaken. Diversity centres are East Himalaja plus Chinese provinces of Yunnan and Sichuan (with diversity maximum of 16.3 in Nepal) and the East African Rift Valley Region (with highest diversity in Malawi, 6.8). Advancement indices of species range from 0.12 to 0.78 within 0 and 1, theoretically possible. The nine most primitive species (AI<0.25) are distributed in Asia and Africa, above an altitude of at least 2, 500 m while in North America most species are highly advanced (AI> 0.65). Correlation analysis with ecological factors such as latitude, altitude, habitat type suggests that the genus originated in the moist montane or alpine zones. © 2002 Akadémiai kiadó Budapest.