Molecular systematics in the genusClintoniaand related taxa based onrbcLandmatKgene sequence data

Abstract

AbstractIn an attempt to elucidate the affinity and phylogeny of the disjunct North American–eastern Asian genusClintonia, two chloroplast genes,rbcLandmatK, were sequenced for all five species (Clintonia andrewsiana, Clintonia borealis, Clintonia umbellulata, Clintonia unifloraandClintonia udensis). Similar sequence data sets for both genes supported the idea that a monophyly ofClintoniaconsists 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 theClintoniatrees,Cardiocrinum(=Lilium)cordatum,Medeola virginiana,Scoliopus bigeloviiandScoliopus halliiwere used as outgroup taxa. Similar topologies forClintoniaresulted when both therbcLandmatKgene sequences were combined. However, when an amino acid tree was generated for thematKsequence, 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 inClintoniawere 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 toClintoniawas also attempted based on the molecular analyses and outgroup analysis, andMedeola virginianafrom eastern North America turned out to be the closest relative found.