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.
Nymphoides peltatum = Villarsia nymphaeoides, Vent.). - The habitat of this plant is still waters, and rivers. The plant has the aquatic habit, with floating leaves, and submerged stems. The rootstock is creeping, with alternate leaves. The flowering stems are floating, with short branches in the axils of opposite leaves. The stems are long, round, branched. The leaves are floating, round, or heart-shaped at the base, stalked, entire, green, shining, with purple spots, purplish, with glands below, with wavy border. The radical leaves are long-stalked, slender, without sheaths, those of the floating leaves not so long, stout, with sheaths. The flowers are yellow. The flower-stalks bear a single flower, and are clustered, crowded. The flowers are more or less umbel-like, and open successively. The sepals are linear to oblong, blunt. The corolla has the lobes fringed with hairs, notched, or fimbriate. The fruit, a capsule, is like a flagon in shape, 3-valved, green. The seeds are few, winged, fringed with hairs. The plant is floating, flowering in July and August, and is a herbaceous perennial.