This section is from the book "British Wild Flowers - In Their Natural Haunts Vol5-6", by A. R. Horwood. Also available from Amazon: A British Wild Flowers In Their Natural Haunts.
The habitat of this plant is sandy and gravelly edges of lakes and ponds, sometimes below water, when it is barren. The habit is tufted. The plant is smooth or downy, and may form a matted mass when submerged. The rootstock is white, creeping, and bears stolons. The leaves, which are all radical, are linear to awl-like, sheathing below, fleshy, channelled, sometimes having hair above. The plant is monoecious. The flowers are white. The male flowers are borne on an axillary scape, not so long as the leaves, and are solitary, and stalked (1-2 in.), with 1-2 bracts below the middle. The sepals are green, with membranous edges, blunt. The female flowers are more or less stalked, with lance-shaped bracts. The fruit is bony, with erect seeds. The plant is 1-3 in. in height. It flowers in August, and is a herbaceous perennial.