Phylogenetic Relationship and Morphology of Dalzellia Gracilis (podostemaceae, Subfamily Tristichoideae) with Proposal of a New Genus

Dalzellia gracilis, an enigmatic species of Podostemaceae, is characterized by the subcylindrical creeping roots and dorsiventral ribbonlike shoots borne on the roots. To reveal the phylogenetic relationships of D. gracilis, molecular phylogenetic and morphological analyses were performed. A matK tree indicates that it is most likely sister to a clade of its congeners and Indotristicha ramosissima. Dalzellia gracilis, like Tristicha, has subcylindrical, capless roots, and it exhibits an endogenous developmental pattern in both shoots and associated holdfasts shared by Terniopsis, Indotristicha, and Tristicha. The dorsiventral ribbonlike adventitious shoots, with the dorsiventral compressed shoot apical meristem producing dimorphic leaves on the dorsal and ventral-lateral sides, are extremely similar to the crustose shoots of the other species of Dalzellia. Dalzellia gracilis is devoid of rosettes, although the other congeners have them. The many free leaves subtending the base of the pedicel are also unique to the species, whereas the trimerous flower is common to subfamily Tristichoideae. On the basis of these molecular and morphological results, we describe a new genus Indodalzellia for D. gracilis to draw attention to these morphological distinctions. Dalzellia, Indodalzellia, and Indotristicha have remarkable morphological differences compared to the inconspicuous morphological diversity in Tristicha and Terniopsis and between the two genera.