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.
Waterwort (Elatine hexar.dra, D.C - The habitat of this plant is margins of ponds, lakes, pools. The plant is of aquatic habit. The stems form a matted mass under water, and are limp, rooting at the nodes. The plant is creeping, and very small. The leaves are opposite, longer than the leaf-stalks, spoon-shaped. The flowers are rose-colour, have the parts in threes, borne on short stalks, in the axils, alternate. The calyx is 3-fid, with unequal sepals. There are 3 inversely ovate petals, longer than the sepals. The stamens are 6 in number. The capsule is top-shaped, with 8-12 straight seeds, which are ascending, the capsule concave above, 3-celled. The plant is 1-3 in. in height, and flowers between July and September, being a herbaceous annual.
The habitat of this plant is muddy ponds. The habit is as in the last. The plant is small and creeping. The leaves are opposite, not so long as the leaf-stalks. The flowers are rose-colour, the parts in fours, stalk-less, with 8 stamens, the calyx 4-fid, and with 4 ovate petals. The capsule is nearly round, depressed, 4-celled. The seeds are curved, nearly double, pendulous, hooked, 4 in each cell. The plant is floating or submerged, 1-3 in. high, flowering in July and August, and is a herbaceous annual.