The duckweed Wolffia microscopica: A unique aquatic monocot

Abstract

The rediscovered species Wolffia microscopica (Griff.) Kurz, endemic to India, Pakistan and Bangladesh, shows several features that make it unique in comparison to other duckweeds, even to other species of the genus Wolffia. During vegetative propagation, the daughter fronds are produced by budding within a single pouch of the mother frond. Several generations of fronds and their initials exist in union with the parent frond at a given time. Most strikingly, almost all the fronds flower, both in nature and under controlled culture conditions. Thus, in contrast to all other duckweed species, generative propagation is as important as vegetative propagation, which opens the opportunity for artificial breeding. Moreover, flower development on both mother and daughter fronds was observed at the same time. In contrast to all other duckweed species, fronds of W. microscopica often possess a ventral projection of varying length ranging from an almost flat appearance of the ventral surface to a length of 4mm. Absence of root cap, root hairs and vascular tissue demonstrate that this ventral protrusion is not a root and accordingly we name this special structure “pseudoroot”. The high number of chloroplasts in the pseudoroot may result in higher capacity of photosynthesis without increasing the frond area which covers the water surface. Thus we propose that the pseudoroot serves to be advantageous to W. microscopica in multiplying at a faster rate in comparison to other duckweeds.