Variation in Populations of Tribulus terrestris (Zygophyllaceae) .3. Isozyme Analysis

Isozyme variation in seedlings was investigated as part of a study to identify the origins of the widespread weed and potential biological control target Tribulus terrestris L. s.1. (Zygophyllaceae). Seedlings were obtained from 30 Australian and 24 overseas collections of burrs. Polymorphism was detected in 8 of the 11 putative loci scored. Queensland and Northern Territory collections differed from other Australian and non-Australian collections, indicating that they belong to a separate and possibly native Australian species. Other Australian collections had a high genetic similarity to burrs obtained from the Mediterranean, West Asia, South Africa, Namibia and the USA, the latter being an introduced population. Two Namibian collections formed a separate group and it is possible that southern Africa, like Australia, has native and introduced plants of T. terrestris. All Indian and two Kuwait collections were grouped together and had little similarity with any other group. Tribulus terrestris in southern Australia is most likely to have originated in the Mediterranean or West Asian region.