Hybridization and introgression in Carpobrotus spp. (Aizoaceae) in California. I. Morphological evidence.

Individuals of the invasive non-native plant species Carpobrotus edulis, its native or naturalized congener C. chilensis, and putative hybrids are found throughout coastal California. This study characterized morphological variation within the genus and assessed the extent of hybridization and direction of introgression between C. edulis and C. chilensis. Twelve randomly selected Carpobrotus individuals from each of 49 sample locations were classified as "C. edulis," "C. chilensis," or one of three intermediate morphotype classes, and compared for clonal, vegetative, and fruit characters. Univariate comparisons showed that C. edulis individuals had deeper mats with more cover within the mat boundary, longer, wider, more serrate leaves, and wider fruits with more carpels than intermediate and C. chilensis morphotype classes. Carpobrotus edulis and intermediates had more lateral branches than did C. chilensis, suggesting that hybrids tend to vary toward C. edulis. Discriminant function analysis (DFA) identified the following characters as discriminating significantly among Carpobrotus groups: leaf length, leaf width, leaf length/width, number of lateral branches, number of carpels, and fruit diameter. Using these characters, DFA correctly classified 98% of apparently pure C. edulis and C. chilensis, but only 76% of all Carpobrotus individuals when putative hybrids were included. Principal components analysis showed that C. edulis and C. chilensis cluster into distinct morphotypes, but that hybrids overlap with both groups, particularly with C. edulis. The genus Carpobrotus in California resembles a large hybrid swarm, with putative hybrids forming a large portion of the overall population and tending to vary toward C. edulis.