- Name also: Common Frogbit, European Frog-bit, European Frog’s-bit
- Family: Frogbit Family – Hydrocharitaceae
- Growing form: Perennial herb. Free-floating water plant, sometimes in shallow water weakly rooted to the bed. Roots long, branched. With runners.
- Height: 2–10 cm (0.8–4 in.). Stem short.
- Flower: Plant dioecious (pistillate and staminate flowers on different plants). Corolla regular (actinomorphic), white; petals 3, obovate, base yellow-spotted, 10–13 mm (0.4–0.52 in.) long. Sepals 3. Stamens 12(–18). Pistil of 6 fused carpels, styles 6, stigmas divided in 2. Flowers axillary in scale-like upper leaves, long-stalked, pistillate flowers solitary, staminate flowers usually in groups of 1–4. Blooms quite rarely.
- Leaves: Long-stalked floating leaves as a rosette, stipulate, stipules big. Blade round–kidney-shaped, cordate-based, with entire margins, 2–5 cm (0.8–2 in) broad, leathery, top green, shiny, underside reddish. Rosette base with 2 thin, scale-like bracts, flowering stems with 1–2 scale-like upper leaves.
- Fruit: Capsule. Fruit probably doesn’t develop in Finland.
- Habitat: Sheltered bays in very nutritious lakes, nutritious ponds, rivers, ditches.
- Flowering time: July–August.
Frogbit is a free-floating water plant, which can loosely attach itself to the muddy bed in shallow water. The species’ natural habitats are overgrown forest ponds and rich bird-waters, where it thrives mostly among cane grass and in inlets where it is protected from the wind and waves. The species grows widely in Finland’s coastal areas, and inland it is centred around south-western Finland and more northern habitats as far as Kemi on the Lapland border. Frogbit isn’t very common anywhere, but like many other demanding water plants it has become more common as the water system has become richer. Frogbit has also exploited forestry, because the extra nutrition that drainage brings and the lowering of water levels created more suitable habitats for it to grow in.
Frogbit’s leaves sometimes provide cover for frogs, damp dwelling places and the white flowers in particular are very decorative on the water on the rare occasions that they appear. Frogbit flowers rarely in Finland, only during very warm summers, so its seeds are not a particularly important method of propagation. It mainly spreads vegetatively, when the leaf rosettes that have grown from the runners break off from the mother plant. After winter the water level rises and the buds that have overwintered can travel on the spring floods and even longer distances with water fowl. This relatively large plant has never managed to spread to pools on bird rocks in the outer archipelago.