RIZWAN Y. HASHMI & SAOOD OMER

Lemna aequinoctialis Illustration Credit: M. Rafiq

Small or minute annual to perennial aquatic thalloid floating or submerged fresh water herbs. Fronds small or grain like, simple, symmetrical or asymmetrical, flat, curved or suborbicular; stem and leaves undifferentiated. Root simple, 1-many on ventral surface of fronds or absent; root hairs absent. Plants monoecious; inflorescence minute; developing in a pouch or pit, enclosed by spathe or without spathe. Staminate flowers 2 or 1, anthers 4 or 2-thecous, pistillate flowers solitary; style very short; stigma concave. Placentation basal, 1-6 ovules. Fruits ribbed or ± smooth and ellipsoid. Flowering erratic. Re-production usually vegetative; daughter fronds budding from a lateral pocket or terminal pit, often remaining attached to the parents. Turions (resting buds) sometimes produced in adverse conditions.

The duckweed family consists of 4 genera and c. 30 species, distributed in still and stagnant waters,. mostly throughout warmer regions of the world, represented in Pakistan by 3 genera and 10 species.

Acknowledgements: We are grateful to the authorities of Royal Botanic Gardens, Kew, for sending the specimens on loan. Thanks are due to Dr. E. Landolt, Prof. C.D.K. Cook (Zurich) and Mr. I.C. Hedge (Edinburgh) for going through the manuscript and offering valuable suggestions. We are indebted to Dr. C.E. Jarvis (BM) for his help in the typification of some taxa. 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.

Lower Taxa

• Lemna L.
• Spirodela Schleid.
• Wolffia Schleid.