Neglected features of probable taxonomic value in Podostemaceae: The case of Polypleurum

The paper reports on hitherto largely neglected discriminative characters in Polypleurum stylosum, P. elongatum, P. minus, as well as the problematic P. munnarense (Podostemaceae, subfam. Podostemoideae) from India and Sri Lanka. The characters discussed include dimorphism of floriferous and vegetative shoots, leaf dimorphism, presence of peculiar floating trichomes on vegetative leaves, and presence of silica bodies in root and shoot tissue. In addition, anatomical pecularities (well-developed cuticle covering the ovary and ovules, cell inclusions in the form of droplets, and presence of idioblasts with firm inclusions of unknown compounds) and specific morphological features (presence of an apical septum in the gynoecium) are documented. All these features point to different developmental and physiological properties of the species concerned, thus signaling separate evolutionary pathways. They may help to elucidate phylogenetic relationships at various taxonomic levels and may prove useful for the delimitation of the genus.