- Name also: Lamb’s Cress, Land Cress, Spring Cress, Hairy Bitter-cress
- Family: Mustard Family – Brassicaceae (Cruciferae)
- Growing form: Annual herb.
- Height: 10–30 cm (4–12 in.). Stem usually glabrous.
- Flower: Corolla regular (actinomorphic), white, approx. 0.5 cm (0.2 in.) across; petals four, 2.5–3 mm (0.1–0.12 in.) long. Sepals 4. Stamens usually 4. Gynoecium fused, a single carpel. Inflorescence an elongating raceme in fruiting stage.
- Leaves: Basal rosette clear, many-leaved, stem leaves alternate, usually 2–4, rosette leaves smaller, stalked, stalk somewhat hairy. Blade pinnate, 1–4-paired, with terminal leaflet, leaflets roundish, terminal leaflet larger than others, kidney-shaped.
- Fruit: Many-seeded, opens lengthwise, slim, flat, 15–25 mm (0.6–1 in.) long, usually backwards-facing siliqua, terminated by a small, often unclear, max. 0.5 mm (0.02 in.) long bristle. Stalk 1/4–1/3 x siliqua length, quite erect.
- Habitat: Dry slopes, juniper meadows, forest margins, pastures, wasteland, crags, rocky outcrops, sometimes as a weed in greenhouses, gardens and lawns.
- Flowering time: May–June.
Hairy bittercress is a characteristic plant in Finland’s south-western archipelago. It thrives as well in shady woodland margins as it does in the open along seashores, rocky ridges with thin soil, and also in land that has been enriched by humans. A frost-free autumn is probably a prerequisite for the plant’s success: annual hairy bittercress sprouts in autumn and flowers the following spring and at the beginning of summer. The archipelago’s mild climate allows the shoots to grow big enough to survive the winter. The species also grows as a weed in gardens and flower boxes. Hairy bittercress does not grow at all in the coldest areas of Europe or those with the most purely continental climates. The plant has spread with traffic all the way to South America and Mexico.
Hairy bittercress can be differentiated from other bittercresses by its dense rosette and the fact that it often has many stems. It is however wise to keep one’s eyes peeled for similar mustard family plants – in 1987 a new species, narrowleaf bittercress (C. impatiens), was found in Finland, in Houtskari in the south-west of the country. The following year a second stand was discovered in Lohjansaari in Karjalohja. In the wild in Finland the plant can be a leftover from a time when the climate was more to its liking. Its Finnish habitats are on islands whose favourable micro-climate plays a role in helping the plant survive and thrive. The number of separate narrowleaf bittercress habitats varies a lot, and it can’t be relied upon to grow every year in the same spots. The cutting of forests and other changes in its habitats are a threat to its survival, even if it is protected. Narrowleaf bittercress lacks the rosette that is typical of Finnish pod-plants, and it can be differentiated from other rosetteless species by its leaves’ clear stipules.