BIOSYSTEMATIC STUDY OF LASTHENIA-CALIFORNICA (ASTERACEAE)

This study examined variation in morphology and isozymes for 36 populations of Lasthenia californica representing the entire range of the species. These and previous results suggest the formation of two geographical races based on pappus shape, isozymes, and flavonoid chemistry. The races appear to coexist in a population examined in more detail (Jasper Ridge). Genetic parameters indicating differentiation within and among populations suggest reduction in pollen and seed movement within the Jasper Ridge population (G(st) = 0.417; Nm = 0.350) and among populations (G(st) = 0.36; Nm = 0.439) of L. californica. In spite of the considerable differentiation among the populations for pappus shape, flavonoid chemistry, and isozymes, there is no indication that the populations could be recognized as taxonomic groups as suggested in earlier taxonomic treatments. The patterns of variation observed in this study are further complicated by the presence of three cytotypes, none of which could be distinguished by the data sets examined. The isozyme study suggests that tetraploid populations are of autopolyploid origin. The only hexaploid population sampled was not analysed for isozyme variation. We believe that the patterns of variation observed in L. californica best fit the model of geographical speciation. The pattern of variation observed at Jasper Ridge suggests that this population might have been established by two colonists-one a northern type and the other a southern type-representing the two geographical races.