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 pools, ditches, streams, ponds, still and slow-flowing- water. The plant is not common. The plant, which is dark-green, has the aquatic habit. It is of the submerged type. The stem is submerged. There are no floating leaves. The leaves are small, not stalked, rounded, with rigid lobes in one plane, thrice forked, sheathing, without auricles, and they form a flat rigid disk. The flowers are white, small, with numerous veins, twice as long as the sepals. The receptacle is hairy, not so wide as the flower-stalk. The buds are flattened at the top. There are 15-20 stamens, and they are longer than the pistil. The achenes are flattened, acute. The style, which is slender, falls at length. The plant is submerged. It flowers between June and August, and is a herbaceous perennial.
The habitat of this plant is running streams and rivers. The plant has the aquatic habit. The stems are long, robust, submerged. The leaves are all submerged, with long, rigid, parallel segments, which are few, narrow, tassellike, twice or thrice forked. The leaf-stalks and some of the leaf-segments may reach a length of a foot. They are black, and form rigid tassels. Rarely floating leaves, which are 3 - lobed or divided, the segments shortly-stalked, are found. The stipules are broad and lance - shaped or rounded. The flowers are large, white, yellow at the base. The flower-stalks are tapering, long, and robust. There may be more than 5 petals, and in 2 rows, broadly inversely ovate, with many veins, contiguous, and they do not fall. The receptacle is conical and smooth. There are numerous short stamens. The stigma is cylindrical, short, and thick. The achenes are large, few, turgid. The plant reaches a length of several feet. It is in flower between May and August, and is a herbaceous perennial.
Ranunculus Drouetii, F. Sch. - The habitat of this species is ponds and ditches. It is of aquatic habit. The stem does not rise out of the water. The submerged leaves are light-green, thrice forked, with limp, tassel-like segments. The floating leaves are rare, and disappear, being 3-partite, the segments more or less stalkless, or stalked, wedge-shaped, divided into two. The upper leaves are more or less stalkless. The lateral segments are stalked, not in the same plane, spreading. The leaves collapse when removed from the water. The whole plant is light-green. The stipules are large, auricled. The flowers are white, starlike, small, the petals 5-7, veined, inversely ovate, soon falling. The buds are oblong. The stamens are few, and longer than the stigma. The latter is oblong, the receptacle oblong. The receptacle in fruit is as thick as the flower-stalk. The achenes are inversely ovate. The plant is floating or submerged. The flowers are in bloom in May and June, and the plant is a herbaceous perennial.