CHEMOSYSTEMATIC STUDY OF HYBRIDIZATION IN CALIFORNIAN LIVE OAK - ACORN STEROIDS

Acorns from 85 individuals of Quercus agrifolia and a wislizenii from seven native populations in California were sampled and analysed for steroid composition. The most abundant steroid was beta-sitosterol (83-87%), with campestrol, stigmasterol and DELTA5-avenastenol in small amounts (2-7%) and DELTA7-stigmastenol and DELTA7-avenastenol at very low levels (<1%). Small, but significant differences between the two species were found in campesterol, stigmasterol, DELTA5-avenastenol and beta-sitosterol. Percentage composition of the first three of these steroids was intermediate in three putative hybrid populations. Putative hybrid populations differed from the combined parents in frequency distributions of percentage composition of these steroids providing support for true intermediacy in these populations. Principal components analysis in conjunction with morphological data was used to identify probable hybrid and backcross individuals. Estimates of hybrid frequency indicated highest levels (ca 60%) in the northern range of Q. agrifolia.