Pond Water Crowfoot
- Subspecies: Pond Water-crowfoot (Common Water-crowfoot, ssp. peltatus), Brackish Water-crowfoot (ssp. baudotii)
- Growing form: Perennial water plant.
- Height: 10–250 cm (4–100 in.). Stem light yellowish–green, sparsely branched apart from upper part, 2–4 mm (0.08–0.16 in.) thick.
- Flower: Corolla regular (actinomorphic), white and yellow at base of petals, usually 1–2 cm (0.4–0.8 in.) wide; petals five, 8–15 mm (0.32–0.6 in.) long and sometimes touching (ssp. peltatus) or 6–10 mm long, not touching each other (ssp. baudotii). Nectaries at base of petals pear-shaped (ssp. peltatus) or sickle-shaped (ssp. baudotii). Sepals 4–5, often with blue tips. Stamens 15–30. Gynoecium separate, pistils 30–40. Flowers solitary leaves opposite, long-stalked, above water.
- Leaves: Alternate, stalked, stipulate. Submerged leaf blades 3–5 times lobed, lobes thread-like, quite rigid–quite slack. Intermediate leaves quite rare. Floating leaf blades kidney-shaped–roundish, 3–5-lobed, lateral lobes wider than central lobe (ssp. peltatus) or almost same width (ssp. baudotii), edge sparsely toothed. Floating leaves can be lacking (especially ssp. baudotii).
- Fruit: Sparsely haired when young, glabrous when older, wrinkled surface, wingless (ssp. peltatus) or winged (ssp. baudotii), 1.1–1.2 mm (0.044–0.048 in.) long achene. Achenes often together.
- Habitat: Solid-based beaches, rich lakes on the Åland Islands, clear-water rivers and lakes on mainland Finland.
- Flowering time: June–September.
The white crowfoot flowers that decorate the shoreline are a joy to holiday-home owners because they thrive in virtually the same conditions as swimmers: clear, bright water and a hard gravel or rocky base. Pond water crowfoot is a sign of clean water and it is usually first to disappear if the water starts to become enriched.
Pond water crowfoot is divided into two subspecies, ssp. peltatus, which grows on mainland Finland in clean water, and ssp. baudotii, which favours brackish water at the seaside. Ssp. peltatus grows in the large lakes of central Finland and also alongside big rivers, especially in the north of the country, and in moving water it doesn’t mind the water being a bit muddy. Crowfoot plants also grow in mildly salty brackish water, especially around estuaries and less salty inlets where rushes thrive. Ssp. baudotii requires a minimum of 2.5 promilles or salt to be able to survive. The muddiness of the water in the inner archipelago limits its growth; on the outer archipelago the surge of the sea forces the firmly anchored plant to seek shelter in inlets close to piers, jetties and wavebreakers. Plants that grow in rougher waters are more robust than those that are protected by the inner archipelago.
Common water crowfoot (R. aquatilis) which favours rich waters and ditches is a close relative of pond water crowfoot. Common water crowfoot has two variations, var. aquatilis and var. diffusus. Apart from these, two other crowfoots that grow in Finland in both sweet and brackish water are R. confervoides and fan-leaved water crowfoot (R. circinatus).