| Summary: | Lasthenia californica DC. ex Lindley is an annual, presumably obligate out crossing species and is the most widespread taxon of the 17 species in this mostly Californian genus. A biosystematic study of this complex has shown that this species is polymorphic in its flavonoid chemistry, electrophoretic banding patterns, and morphologyat the intra- and interpopulation levels. A detailed analysis of a population located in the Biological Preserve of Stanford University (Jasper Ridge) showed that there is a strong correlation among flavonoid profiles, pappus morphology and isozyme patterns. A long term study at Jasper Ridge suggests that the spatial distribution of pigment types along several transects has remained essentially constant over a period of 10 years. Indices of genetic differentiation in populations and preliminary findings of breeding experiments also suggest population subdivision and low levels of crossability between plants with different flavonoid profiles. It appears that these forms flower atdifferent times. The pattern of variation observed at Jasper Ridge suggests that the two genotypes represent a northern race and a southern race. It is premature to conclude whether the population structure at Jasper Ridge is unique to this site. Variation in morphology, flavonoid chemistry, and isozymes failed to group the populations of L. californica into recognizable taxonomic categories. However, the character states observed (i.e., in morphology, flavonoids, and isozymes) at Jasper Ridge show a polarized distribution (north-south) in the other 34 populations examined across the species' range and represent geographical races. There is also a positive correlation among the data sets in some populations although this correlation is different than the one observed at Jasper Ridge. Ecological races - one coastal and one inland - were also observed. The formation of various races in the L.californica complex is believed to represent a step toward speciation and it seems that the geographical speciation model best reflects the patterns of variation observed. Diploid, tetraploid, and hexaploid populations are found throughout the range of the species and are indistinguishable geographically, morphologically, chemically or by their allozymes. The isozyme study suggests that the tetraploid populations are of an autopolyploid origin. The only hexaploid population sampled was not analysed for its isozyme variation. === Science, Faculty of === Botany, Department of === Graduate
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