- Family: Butterwort Family – Lentibulariaceae
- Growing form: Perennial herb. Roots thin.
- Height: 10–20 cm (4–8 in.). Stem leafless, especially upper part of scapes (1–6) with glandular hairs.
- Flower: Corolla Irregular (zygomorphic), strongly purple, 15–25 mm (0.6–1 in.) long, fused, bilabiate, spurred. Upper lip 2-lobed, lower lip 3-lobed, spur narrow, curving downwards, about a quarter of corolla length, throat with white spots. Calyx bilabiate, 5-lobed. Stamens 2. Gynoecium composed of 2 fused carpels. Flowers solitary, terminating scapes.
- Leaves: In basal rosette, short-stalked. Blade elliptic, 2–2.5 cm (0.8–1 in.) long, green, edges curling upwards. Sticky leaf surface with glandular hairs and secreting glands.
- Fruit: Yellowish brown, egg-shaped, capsule open at tip.
- Habitat: Fens, springs, shore banks, damp meadows, gravels, damp rock walls.
- Flowering time: June–July.
Genus Pinguicula is comprised of 35–50 plants that grow mainly in Europe, Northern Asia and America. In Finland there are three species: common butterwort, alpine butterwort (P. alpina) and hairy butterwort (P. villosa). Common butterwort’s habitat is mainly in northern Finland and roughly from the bottom of the Bay of Bothnia northwards it is quite common in all kinds of damp places. In southern and central Finland it grows mainly in the eastern part of the country in fen-like bogs, damp meadows, spring margins and coasts. On the Åland Islands it grows sparsely on calciferous meadows. Common butterwort has become rarer in the southern parts of its former habitat because it has less suitable places to grow as a consequence of increased drainage.
Like some of the best-known carnivorous plants, genus Drosera and its related genus Utricularia, butterworts feed themselves by trapping insects. On closer inspection the upper surface of the basal rosette’s leaves seem to be spotted. These glandular hairs secret a sticky glue that traps the prey and enzymes that digest it. Most of the glands are on the middle part of the blade – up to 25,000 per square centimetre – and the plant is able to direct its prey there by turning its leaf margins inwards. In a couple of days all that is left of the insect is the indigestible chitin skin, the wings and the feet. From the part that it can digest common butterwort gets mainly nitrogen, which is otherwise scarce in its habitat. In Scandinavian languages it is known as sour-milk herb because its protein-splitting enzymes were used to curdle milk. Butterworts can survive without insect meals, but they need them in order to pollinate: common butterwort is visited by bumblebees and honeybees. Butterworts overwinter with the help of bulb-like overwintering bulbils and can live for up to ten years.