Common Water Crowfoot
- Name also: White Water-buttercup, Water-crowfoot
- Family: Buttercup Family – Ranunculaceae
- Growing form: Perennial herb. Water plant.
- Height: 10–50 cm (4–20 in.). Stem greenish, branched, often rooting, at least. 1.5 mm (0.06 in.) thick.
- Flower: Corolla regular (actinomorphic), white and base of petals yellow, usually. 1–2 cm (0.4–0.8 in.) wide; petals five, 8–9 mm (0.32–0.36 in.) long, sometimes touching. Nectaries at base of petals sickle-shaped–almost round. Sepals 4–5. Stamens usually 15–20. Gynoecium separate, pistils 15–30. Flowers solitary opposite leaves, long-stalked, above water.
- Leaves: Alternate, stalked, stipulate. Submerged leaves finely lobed, lobes thread-like, straggly, slack. Often with intermediate leaves. Floating leaf blade roundish–kidney-shaped, 3-lobed, lateral lobes wider than central lobe, with long and tapered teeth. Floating leaves can be lacking. Plants on land are short-stalked, with small blades, and with rigid and fleshy lobes.
- Fruit: Hairy when young, glabrous when older, wrinkled surface, sharp-edged, 1.1–1.9 mm (0.044–0.076 in.) long achene, tip with 0.1–0.3 mm (0.004–0.012 in.) long bristle. Achenes often together.
- Habitat: Ditches, ponds, ditches, alder swamps. Often also on wet ground.
- Flowering time: June–July(–August).
Crowfoots form a clearly distinct group of white-flowered water plants within the large Ranunculus family. This where the clarity ends, however. The conditions of the habitat create many variations in crowfoot’s appearance, multiple chromosomes influence how the plant looks, and these variations, which have different genes, cross-breed – cross-breeding between different species is probably relatively common too. It is often frustratingly difficult even for professional botanists who are familiar with the group to deal with it, never mind amateurs.
There are two variations of common water crowfoot that grow in Finland, both of them only in the south of the country. The usual form in rich ditches and ponds is var. aquatilis, which is large-flowered and usually has floating leaves. The other variation, diffusus prefers cooler, moving water and is usually flowerless with submerged leaves. Common water crowfoot can also grow near water on the land, and they can look quite different from plants that grow in water. Although the differences in the ecology of the different forms are clear, telling them apart from other members of the genus is not always easy. Sometimes there have been attempts to group R. confervoides, which is a small, delicate, floating leafless plant that grows mainly in the clear-watered rivers of northern Finland, in as a variation. Apart from the fact that it is smaller in every way, common water crowfoot is also similar to pond water crowfoot (R. peltatus) and commonly cross-breeds with it. Sometimes even the majority of crowfoots in springs are hybrids. The most reliable differences in crowfoots are found in the flowers – unfortunately, however, submerged forms are often completely flowerless.