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Keywords:

  • Clintonia;
  • cpDNA;
  • Liliaceae;
  • Liliales;
  • matK;
  • megasporogenesis;
  • molecular systematics;
  • rbcL

Abstract

In an attempt to elucidate the affinity and phylogeny of the disjunct North American–eastern Asian genus Clintonia, two chloroplast genes, rbcL and matK, were sequenced for all five species (Clintonia andrewsiana, Clintonia borealis, Clintonia umbellulata, Clintonia uniflora and Clintonia udensis). Similar sequence data sets for both genes supported the idea that a monophyly of Clintonia consists of two clades, one in eastern Asia and one in North America. The North American lineage resolves into an eastern group and a western group. There are surprisingly few site substitutions within these two genes, notwithstanding the wide morphological diversity of the genus. To root the Clintonia trees, Cardiocrinum (=Lilium) cordatum, Medeola virginiana, Scoliopus bigelovii and Scoliopus hallii were used as outgroup taxa. Similar topologies for Clintonia resulted when both the rbcL and matK gene sequences were combined. However, when an amino acid tree was generated for the matK sequence, all differences between the North American species were reduced to similarities due to synonymous codon sequences. Differentiation patterns of some selected morphological, karyological and embryological characters in Clintonia were also reviewed in comparison to the resulting molecular topologies. The unique, Clintonia-type megasporogenesis that produced identical, maternally derived, diploid zygotes and endosperm coupled to polyploid buffering provides a considerable constraint on variability. A search of possible sister genera to Clintonia was also attempted based on the molecular analyses and outgroup analysis, and Medeola virginiana from eastern North America turned out to be the closest relative found.