VARIATION IN POPULATIONS OF TRIBULUS-TERRESTRIS (ZYGOPHYLLACEAE) .1. BURR MORPHOLOGY

Variation in bun morphology was investigated as part of a study to ide ntify the origins of the widespread weed and potential biological cont rol target Tribulus terrestris L. s.l. (Zygophyllaceae). Measurements were made of four size variables, four spine angles and the number of seeds in each bun from 31 Australian and overseas collection sites. Cl uster analysis using all variables (valid for 26 collection sites) ide ntified four groups of burrs, one of which contained a single site fro m Israel that differed due to the angle of the spines. All 31 sites we re included by removing the measurement of the basal spine, which is s ometimes absent from burrs. Four clusters were found on reanalysis. Th e minimum number of variables that produced the four clusters were len gth and width of burrs and abaxial spine length. Most southern Austral ian sites were grouped with southern African, Indian and Israeli sites . Three Western Australian sites formed one group, as did Northern Ter ritory and Queensland sites. A fourth group included one site each fro m Australia, Iran, Israel and USA. The relationship between base lengt h and width of the bun distinguished the probably native northern Aust ralian collections, which have either more squat or more elongate burr s, from the probably introduced populations of T. terrestris in southe rn Australia. However, analysis of morphological variation only approx imately detected groupings within the southern Australian and overseas collections that were subsequently identified by isozyme and cytogene tic studies.