Molecular Phylogenetic Analysis of Asarum sect.Euheterotropa Based on Chloroplast trnL/F and Nuclear rDNA ITS Sequences.

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Asarum section Euheterotropa (Aristolochiaceae) is composed of five species endemic to Japan : A.asaroides distributed in northern Kyushu District, A.satsumense in southern Kyushu District, A.curvistigma in Tokai District., A.muramatsui in Izu Peninsula and A.tamaense in Kanto District. Morphologycally, these species share a broad calyx-tube, a complicated annulus and a style with stigma gradually decurrent to its abaxial side, and thereby they have assigned to the same section and regarded to be diversified in spreading to eastern district of Japan (Maekawa, 1953, 1964). However, the two disjunctive species groups appear to differ in origin. In order to clarify the phylogenetic and biogeographical relationships of the five species of section Euheterotrop we investigated molecular phylogeny, using DNA sequences from the chloroplast DNA region (trnL/F) and the internal transcribed spacer (ITS) of nuclear ribosomal DNA. Sequences of the trnL/F were found to be invariable and thus to be not useful in considering the phylogenetic relationships. In contrast, ITS-1 sequences were found to be informative phylogenetically. Two major clades (I and II) were revealed found to be informative phylogenetically. Two major clades (I and II) were species in Kyushu and the other three species in Tokai/Kanto did not form a common clade, and were clearly divided into the above two different clades, respectively. Therefore, it is clear that the five species belonging to the sect.Euheterotropa is not a monophyletic group. The results obtained from the present study do not support the Maekawa's hypothesis.