Lasthenia sect. Baeria, one of six sections recognized by Ornduff (1966) in Lasthenia, includes the most common and geographically widespread goldfield species L. californica. Previous biosystematic studies using morphology, flavonoids, and isozymes have not revealed any unequivocal lineages within this morphologically and ecologically highly variable taxon. Maximum parsimony analysis of DNA sequence data from the internal and external transcribed spacers of 18S-26S nuclear ribosomal DNA, and the 3' end of the matK coding gene and adjacent 3' trnK intron of chloroplast DNA from over 60 populations of L. californica and close relatives yielded a well-supported tree showing that L. sect. Baeria is monophyletic only with the inclusion of L. leptalea, previously placed in L. sect. Burrielia. Most importantly, this tree also resolves L. californica to be a non-monophyletic group that represents two robustly supported clades. One clade includes L. macrantha; the other may be sister to L. sect. Baeria. Each of the two groups can be diagnosed by pappus morphology (although some individuals are epappose) and to some extent by geographic distribution. We have recognized these two clades of L. californica as distinct taxa. The molecular results also show that the overall diversification in the clade corresponding to L. sect. Baeria plus L. leptalea has been accompanied by minimal morphological divergence, which has resulted in previously underappreciated cryptic diversity.

Key words: cryptic diversity, external transcribed spacer, internal transcribed spacer, Lasthenia californica