Molecular phylogeny of Japanese Potamogeton species in light of noncoding chloroplast sequences

In the genus Potamogeton, high morphologic and ecologic diversification and difficulty in evaluating systematic usefulness of various characteristics have led to the definition of many small groups of species corresponding to sections or subsections. The 18 species of Japanese Potamogeton that have high variation represent 11 of the 14 species groups proposed in a recent treatment of the genus. We performed phylogenetic analyses of these 18 species of Japanese Potamogeton with three allied genera by using the noncoding region of chloroplast DNA between trnT (UGU) and trnL (UAA). Our phylogenctic tree revealed that Japanese Potamogeton were divided into two main groups (I and II). In general, each group was characterized by the shape of the submerged leaves and anatomic features of the stem. Group I comprised eight species with broad submerged leaves, and these species lacked sub-epidermal bundles in the stem. Group II comprisesd 10 species characterized by linear submerged leaves and the presence of subepidermal bundles. Group II was further divided into two subgroups (IIa and IIb). Subgroup IIa taxa did not have a dormant period or physiologically specialized turions, and the stele was of the trio or proto-type. In comparison, subgroup IIb members have dormant period in the form of axillary or apical turions, and stele types were oblong or circular. Potamogeton crispus and P. maackianus, each of which has distinct morphology and ecology, are included in group I but differed from the other Potamogeton in having unique length mutations and substitutions in the trnT-trnL sequence. (C) 2004 Elsevier B.V. All rights reserved.