- Name also: Round-leaved Sundew, Roundleaf Sundew
- Family: Sundew Family – Droseraceae
- Growing form: Perennial herb.
- Height: 5–20 cm (2–8 in.). Stem vertical, clearly longer than leaves, straight-based, leafless, red scape.
- Flower: Corolla regular (actinomorphic), white, approx.1 cm =o.4 in.) broad; petals five, 4–6 mm (0.16–0.24 in.) long. Sepals 5. Stamens 5. Gynoecium syncarpous, with 6 styles. Inflorescence, Inflorescence a 3–10-flowered scorpioid cyme. Flowers only open in sunshine.
- Leaves: In basal rosette, long-stalked, red, flush. Blade roundish–kidney-shaped, upper surface with many long, red, slime-excreting glandular hairs.
- Fruit: Pear-shaped, tapering tip, glossy, 4-valved capsule.
- Habitat: Dryish bog-moss surfaces in swamps and bogs, lakeside banks, ditches, sandpits.
- Flowering time: June–July.
Sundews supplement the lack of nitrogen compounds in their barren bog moss habitats and are probably among the best-known carnivores in Finland. Although they can survive without their insect food, the most successful hunters grow large and flower abundantly. Their prey amounts to around one creature per month, usually mosquitoes or smaller insects, but occasionally dragonflies or butterflies can fall victim.
An insect that lands on a sundew leaf gets trapped by the sticky liquid that is secreted by the plant’s glandular hairs, and the more it struggles the more stuck it becomes. The hairs bend at the point of contact, and if there is enough irritation the whole leaf blade will begin to curl up. The same reaction can be achieved with a small piece of meat or something else with a high protein content. Wood chips and other rubbish will also make the plant initially react, but it soon notices the deception. The glandular hairs excrete the same kind of enzymes as the human digestive system, and the soft parts of the prey dissolve to be ingested by the plant. After the plant has enjoyed its meal the leaf extends and the undigested chitin leftovers are blown away by the wind and rain.
Sundews have been used in folk medicine to heal e.g. corns and whooping cough – and they are still collected as an ingredient in cough medicine. Common sundew is the most common of the three sundew species that grow in Finland. In northern Finland it favours nutritious growing places but further south it tends to avoid these. The largest of the Finnish sundews is great sundew (D. anglica), which can be differentiated from common sundew by its narrower, oblanceolate leaves. The third sundew is oblong-leaved sundew (also named as spoonleaf sundew, Drosera intermedia), which grows in the south of Finland and is classed as endangered. Its leaves are between round and long, but it can be told apart by its curve-based flowering scape.