Morphology suggests that the Californian annual Microseris douglasii is a monophyletic sister group to the other three diploid annuals of Mictvseris. Phylogenetic analysis of 44 inbred strains of M. douglasii derived from 23 populations with 72 RAPD markers in the nuclear DNA strongly supports this phylogeny. However, 13 chloroplast RFLPs divide M. douglasii into four distinct groups. Two of these each share one or more cpRFLPs with M. bigelovii and M. pygmaea. Several hypotheses can explain

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... incongruence between nuclear and chloroplast phylogeny: (1) random sorting out of chloroplasts during phylogeny from a polymorphic pool, (2) cytoplasmic introgression from the related annual M. bigelovii into M. douglasii after hybridization followed by elimination of the M. bigelovii nuclear genome. We suggest cytoplasmic introgression as the most likely origin. Possible remnants of nuclear introgression have been found in two populations of M. douglasii that are polymorphic for chloroplast types. In these populations M. bigelovii type chloroplast DNA seems to be accompanied by nuclear genes for flower color and leaf shape. Recent studies about disagreement between nuclear and chloroplast-based phylogenies have provided potential evidence for reticulate evolution (RmSEBERG 1991). Allopolyploids are clear evidence of a reticulate pattern, and chloroplast data often reveal the maternal contribution to the original hybridization event,