Comparative morphology and molecular systematics of Podostemum (including Crenias) American river-weeds (Podostemaceae)
Moline, Philip M.; Les, Don; Philbrick, C. Thomas Novelo R.; Pfeifer, Evelin; Rutishauser, Rolf
published: Oct 9, 2006
Podostemaceae live as haptophytes in swift-running rivers with stony beds and seasonally changing water levels, mainly in the Tropics. The present study provides a comparative morphological study of eight Podostemum spp. including the former genus Crenias (P. comatum, P. distichum, P. irgangii, P. muelleri, P. ovatum, P. rutifolium, P. scaturiginum and P. weddellianum), as well as a phylogenetic analysis including P. ceratophyllum of nrDNA (ITS) and trnK intron sequences to infer the infrageneric classification of Podostemum. Twenty-seven morphological characters were coded in a data matrix and used for a cladistic analysis in combination with molecular data. Emphasis is given to the stipule types and how they are attached to the obliquely inserted leaf sheaths. A monophyletic group is formed by P. ceratophyllum, P. comatum, P. muelleri, P. rutifolium, and species of the former genus Crenias (i.e. P. ovatum, P. scaturiginum and P. weddellianum). This suggests that Podostemum (with ribbed capsules, two linear stigmas, short stigmatic papillae) is paraphyletic without the inclusion of Crenias (characterized by smooth capsules, mainly two palmately branched stigmas, and hairlike stigmatic papillae). The "Crenias" species investigated appear as sister clade to Podostemum. except Podostemum distichum and P. irgangii which are sister to the remainder of Podostemum and "Crenias". The phylogenetic analysis confirms a close relationship of P. distichum and P. irgangii. These species share the tendencies to increase the number of stipular lobes (axillary teeth) per leaf and to produce three-dimensional compound leaves with whorls or pseudo-whorls of scales along the rachides.