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 shallow lakes. The plant is tufted in habit. The rootstock is creeping, with cellular, white roots of jointed fibres. The leaves are awl-like, flattened at the margin, green, translucent, septate, smooth. The flowers are unisexual, borne on a scape, twisted, with 6-8 furrows, longer than the leaves. The flowers are 4-cleft, hairy at the end, as well as the scales, in a compact scaly head. The fertile flowers are 4-partite. The parts are in twos, the outer segments being dark, bearded at the tip, the inner fringed with hairs with a black spot at the tip. The lateral flowers have the divisions keeled, flattened, blunt, fringed. Each flower has a scale, black and blunt, shorter and broader. The anthers are dark. The ovary is stalked. The capsule is 2-celled. The plant is 6 in. to 2 ft. high, flowering in July and August, and is a herbaceous perennial.