Trapaceae , nom. cons., (Hydrocaryaceae).
National Herbarium, Agricultural Research Council, Rawalpindi.
Annual hydrophytes. Floating leaves alternate, rosulate, stipulate; stipules caducous; lamina deltoid to rhomboidal; petiole spongy, dilated. Submerged leaves opposite, dissected, root-like, chlorophyllous. Flowers tetramerous, solitary in the axils of floating leaves. Calyx adnate to the ovary, persistent, becoming hard and spinescent in fruit. Petals and stamens inserted round a disc. Ovary semi-inferior, bi-locular, uni-ovuled. Fruit a quadrangular nut with 2 or 4 spines, developed from the persistent calyx.
A unigeneric family, included under Onagraceae in older books. (C.B. Clarke in Hook. f., Fl. Brit. Ind. 2:590.1879; Cooke, Fl. Bomb. 1:551. 1903). Differs markedly from it by its totally hydrophytic habit, semi-inferior ovary and spiny fruit.
The family has an unusual seed germination process, where only one of the two unequal cotyledons takes part.
Acknowledgements: We are grateful to the United States Department of Agriculture for financing this research under P.L. 480 and to Messrs. B.L. Burtt, I.C. Hedge and Miss J. Lamond of the Royal Botanic Garden, Edinburgh, Mr. S. A. Khan of the Pakistan Forest Institute, Peshawar, for giving valuable suggestions and Dr. A.R. Beg, Forest Botanist, Pakistan Forest Institute, Peshawar, for the loan of the material.