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 c ontrol target Tribulus terrestris L. s.l. (Zygophyllaceae). Seedlings were obtained from 30 Australian and 24 overseas collections of burrs. Polymorphism was detected in 8 of the 11 putative loci scored. Queens land and Northern Territory collections differed from other Australian and non-Australian collections, indicating that they belong to a sepa rate and possibly native Australian species. Other Australian collecti ons had a high genetic similarity to burrs obtained from the Mediterra nean, West Asia, South Africa, Namibia and the USA, the latter being a n introduced population. Two Namibian collections formed a separate gr oup and it is possible that southern Africa, like Australia, has nativ e and introduced plants of T. terrestris. All Indian and two Kuwait co llections were grouped together and had little similarity with any oth er group. Tribulus terrestris in southern Australia is most likely to have originated in the Mediterranean or West Asian region.