Systematic Implications of Chloroplast DNA Variation in the Genus Microseris (Asteraceae: Lactuceae)

Abstract

Chloroplast DNA restriction site variation was examined for all 16 species of Microseris, using 22 restriction endonucleases, filter hybridization experiments, and comparative mapping procedures. Mutations were scored relative to other genera of the subtribe Microseridinae, and related genera of the tribe Lactuceae. A total of 115 restriction site mutations was detected, 78 of which were phylogenetically informative. A single most parsimonious cladogram was constructed which indicates three major lines of evolution within the genus. The morphologically distinct annual M. lindleyi was found to be the most divergent and forms the basal lineage within the genus. Forty-three mutations separate annual and perennial species of the genus, whose average sequence divergence is 0.7%. The parentage of the allotetraploid species M. heterocarpa was confirmed, utilizing cpDNA and nuclear ribosomal DNA variation. Evaluation of relative rates of cpDNA evolution indicates that generation time is not responsible for unequal rates of cpDNA in different lineages. The results also suggest that a taxonomic reevaluation of Microseris at the subgeneric level is war- ranted. Microseris D. Don is comprised of 16 species