RIZWAN Y. HASHMI & SAOOD OMER
Department of Botany, University of Karachi, Karachi-32
Dioecious or monoecious, annual, submerged aquatic fragile herbs, rooting at the base and from lower nodes. Stems elongated, slender, much branched, occasionally spiny. Leaves sessile, in pseudo-whorls, linear, linear-oblong, spinous dentate or serrate at margins, occasionally spinous on upper surface of the midrib. Sheath rounded, to more or less auricled or truncate in the upper part. Flowers unisexual, axillary, solitary or few in axillary shoots, often enclosed in a membranous spathe which tapers at the top, the edge mostly provided with few dentations, or spathe absent. Male flowers enclosed by 2-lipped perianth; anther subsessile, 1 or 4-thecous, basifixed, slightly open at the apex. Female flowers without perianth, ovary subsessile, 1-locular, with 1 basal erect anatropous ovule; style cylindrical; stigmas 2-3. Fruit indehiscent; seed with hard testa, surface areolated; embryo straight, without endosperm.
Unigeneric family with c. 40 species distributed throughout the world in fresh and brackish water habitats.
Acknowledgements: We are grateful to the authorities of Royal Botanic Gardens, Kew, for sending the specimens on loan. Thanks are due to Dr. L. Triest (Brussels), Mr. I.C. Hedge (Edinburgh) and Prof. C.D.K. Cook (Zurich) for going through the manuscript and offering valuable suggestions. The financial assistance received from United States Department of Agriculture under PL-480 programme with the coordination of Pakistan Agricultural Research Council, Islamabad, is thankfully acknowledged.