Comparison of chloroplast and nuclear phylogeny in the autogamous annualMicroseris douglasii (Asteraceae: Lactuceae)

Morphology suggests that the Californian annualMicroseris douglasii is a monophyletic sister group to the other three diploid annuals ofMicroseris. Phylogenetic analysis of 44 inbred strains ofM. douglasii derived from 23 populations with 72 RAPD markers in the nuclear DNA strongly supports this phylogeny. However, 13 chloroplast RFLPs divideM. douglasii into four distinct groups. Two of these each share one or more cpRFLPs withM. bigelovii andM. pygmaea. Several hypotheses can explain the incongruence between nuclear and chloroplast phylogeny: (1) random sorting out of chloroplasts during phylogeny from a polymorphic pool, (2) cytoplasmic introgression from the related annualM. bigelovii intoM. douglasii after hybridization followed by elimination of theM. bigelovii nuclear genome. We suggest cytoplasmic introgression as the most likely origin. Possible remnants of nuclear introgression have been found in two populations ofM. douglasii that are polymorphic for chloroplast types. In these populationsM. bigelovii type chloroplast DNA seems to be accompanied by nuclear genes for flower color and leaf shape.