| Intergeneric and interspecific relationships of Aster sensu lato and related genera were studied using data from restriction site analysis of chloroplast DNA. Total DNAs from 48 taxa of Aster s.l. and nine taxa from Erigeron, Solidago and Heterotheca were extracted and digested with 10 restriction enzymes. Representatives of the following genera and subgenera of Aster s.l. were included in the analysis: Almutaster, Amellastrum, Biotia, Brachyactis, Doellingeria, Erigerastrum, Eucephalus, Heleastrum, Ionactis, Oclemena, Oreostemma, Sericocarpus, Symphyotrichum, Virgulus, and Weberaster. Nine lettuce chloroplast DNA SacI fragments were used as probes for Southern blot hybridization. The data were analyzed with PAUP by Wagner methods and Dollo methods using Erigeron or Solidago as the outgroup. The molecular data provided strong evidence that Aster s.l. is polyphyletic. The virguloid (x = 5; Virgulus), oxytripolioid (x = 5; Tripolium), dumosoid (x = 8; Symphyotrichum) and conyzopsoid asters (x = 7; Brachyactis) were closely related and shared a common ancestry with some x = 9 species (Weberaster). This group was very distinct from Aster sensu stricto. Some x = 9 species complexes (Amellastrum, Doellingeria, Eucephalus, Ionactis, Oclemena, Oreostemma) recognized in taxonomic treatments at the subgeneric or sectional level, grouped closer to Solidago or Erigeron than to typical Aster (including Biotia, Heleastrum and Sericocarpus) and the lower base number species. The taxonomic positions of some species remain unresolved based on RFLP analysis of cpDNA. As many as twelve genera could be recognized, although some of these could be combined; Aster, "Amellastrum", Doellingeria, Eucephalus, Ionactis, "Oclemena", Oreostemma, Symphyotrichum, Tripolium, Virgulaster. Virgulus, and Weberaster. Further studies using gene-sequencing data which are from cpDNA ndhF and matK and 5S, 16-26S and ITS of nuclear ribosomal DNA are essential to clarify the phylogeny of all species groups placed in Aster by recent authors.;In the present study, several other topics, such as nucleotide divergence of cpDNA in asters, Wagner parsimony and Dollo parsimony, basic chromosome numbers in asters, are also discussed. In this study, it was found that the Wagner parsimony is more accurate than the Dollo method in producing phylognetic trees. Also, based on the evidence gathered here, it appears that the basic chromosome number in the asters is x = 9. In future systematic studies on the asters, restriction site analyses of both cpDNA and rDNA will be needed to fully elucidate the origin and evolution of polyploids in the genus Aster s.l. |
