Studies on the Morphology and In Vitro Seed Germination of Polypleurum stylosum var. laciniata (Podostemaceae)

Abstract

Polypleurum stylosum var. laciniata of the family Podostemaceae, is an endemic aquatic angiosperm, which grows on rocks in fast flowing rivers and streams in Kerala (India). The plant body is thalloid and it lacks the conventional differentiation into root and shoot and is attached to the rocks with the help of rhizoids. Vegetative growth occurs in submerged conditions and lowering of water table triggers flowering. Flower buds appear along the thallus margin enclosed by a spathella and sustained by two or three pairs of bracts. The ovary lacks a distinct style and the stigma is characteristically bifid. There are two stamens with their filaments fused, which keep on elongating and mingle with the stigma at maturity. High pollen–ovule and ovule–seed ratio indicate the high probability of plant establishment. Nearly 205 minute seeds are produced in a fruit. The embryo lacks plumule and radicle. In tissue culture, the seeds germinate and produce a green radical which sticks to the hard substratum by means of the epidermal outgrowths. The main thalloid plant body originates from the hypocotyl region as a bulge and grows into a prostrate branched thallus.