- Written also: Large Bitter-cress
- Family: Mustard Family – Brassicaceae (Cruciferae)
- Growing form: Perennial herb. With runners.
- Height: 20–40 cm (8–16 in.). Stem sparsely branched, bristly, glabrous, hollow.
- Flower: Corolla regular (actinomorphic), white (occasionally reddish), approx. 1.5 cm (0.6 in.) wide; petals four, 7–9 mm (0.27–0.35 in.) long. Sepals 4. Stamens usually 6, of which 4 long and 2 short, anthers dark purple. Gynoecium fused, a single carpel. Inflorescence a raceme, extending in fruiting stage.
- Leaves: Lacking basal rosette. Stem leaves alternate, basal leaves long-stalked, upper stem leaves almost stalkless. Blade pinnate, 2–5-paired, terminal leaflet. Upper and lower leaves’ leaflets with same shape, elliptic, with toothed or curved margins, bright green, glabrous.
- Fruit: Many-seeded, opening lengthwise, slim, flat, 2–3 cm (0.8–1.2 in.) long, erect siliqua.
- Habitat: Springs, swamps, shoreside hedgerows, stream banks, rocky rapids, ditch banks, also in water.
- Flowering time: May–June.
Large bittercress is one of the better Finnish wild plants for indicating the presence of groundwater. It is best to look for it in places where springs babble forth or iron sulphide gives the spring water a rusty colour. Springs are not always visible to the eye: it is common that water only trickles gradually to the surface. Large bittercress can also grow as a reminder of springs that have since dried up: the species is very tenacious in places that people have disturbed, although a ditchbank is not as good a habitat as a spring. The movement of water is essential: on one hand it provides an unceasing flow of nutrients and on the other hand the moving water doesn’t freeze and keeps the rootstock free of frost throughout the winter. The species stays green throughout the winter so it is ready to flower early the following spring. Large bittercress is usually self-pollinating and rarely produces fruit. It usually spreads vegetatively through pieces of runner that break off.
Large bittercress grows in Finland at the northern limit of its habitat. In Finland it can mainly be found in part of Satakunta, southern parts of southern Häme, and it grows rarely in western parts of Uusimaa. It is entirely absent from the south-west coast and the Åland Islands. The northernmost separate stands are around Kuopio. Although large bittercress is on the rare side in Finland and tastes quite bitter, according to a few local names it has been eaten in salads.
Large bittercress looks quite a lot like cuckoo flower (C. pratensis). The species differ from each other with regards to cuckoo flower’s rosette leaves, whose leaflets are different shapes and sizes compared to the stem leaves. Flowering large bittercress flowers are virtually always pure white, lacking the purple hue that is common to cuckoo flower; also, large bittercress’s anthers are purple while cuckoo flower’s are yellow.