- Name also: Keek, Yellow Fieldcress, Yellow Field Cress, Creeping Yellow Cress, Creeping Yellow-cress
- Family: Mustard Family – Brassicaceae (Cruciferae)
- Growing form: Perennial herb. Rhizomatous, forms stands.
- Height: 20–50 cm (8–20 in.). With abundant runners.
- Flower: Corolla regular (actinomorphic), yellow, approx. 1 cm (0.4 in.) wide; petals four, 4–5 mm (0.16–0.2 in.) long. Sepals 4, approx. half length of calyx. Stamens 6, of which 2 short and 4 long. Gynoecium fused, a single carpel. Inflorescence a raceme, extending in fruiting stage.
- Leaves: Alternate, stalked, exstipulate. Blade pinnately lobed(–with leaflets), usually glabrous, pale green, lobes 4–7 pairs, narrow, with toothed margins, commonly twice-lobed, terminal lobe no larger than other lobes.
- Fruit: Many-seeded, linear, slightly arching, 8–18 mm (0.32–0.72 in.) long siliqua, tip with approx. 1 mm (0.04 in.) long bristle. Stalk approx. 10 mm (0.4 in.), spreading–slightly ascending oblique. Seeds often fail to develop.
- Habitat: Gardens, flower beds, nurseries, park lawns, roadside embankments, waste ground, ditches, river banks beside arable ground.
- Flowering time: June–August.
- Harmfulness: Harmful invasive species.
Creeping yellowcress is probably native to the European broad-leaved forest belt. Feral stands are difficult to trace because human activity has changed them a lot a long time ago. On the other hand the species has spread with people around the world. The first information about it growing in Finland is from the middle of the 19th century, but at that time it was limited to harbours and ballast soil deposits from sailing boats. Creeping yellowcress began to become more abundant towards the end of the 19th century, when suburbs began to be built quickly and the species found a lot of new habitats in the planted areas and a lot of other places where the earth was disturbed. The species spreads mainly vegetatively and has therefore colonized Finland more slowly than other species that spread by seed, but it was still one of the most actively spreading species from the 20th century. Nowadays it is common on the Åland Islands and the south coast, but it becomes rarer inland even if it seems to be becoming more common there. The northernmost limit of its habitat is in Kuusamo.
Creeping yellowcress sometimes grows as a field weed, but it is much more of a nuisance in young plant nurseries. Its dense and large creeping rootstock spreads widely and it is able to grow from pieces of it so it is not easy to eradicate. Stands of creeping yellowcress can cover the ground and choke the life out of any young shoots, and it spreads easily to new habitats in clumps of tree and hedge roots. From planted areas and waste ground it has spread to roadsides, shores and even clearings in common alder woods.
Marsh yellowcress (R. palustris) is native to Finland and it differs from creeping yellowcress with regards to e.g. the way that its terminal lobe is larger than the rest. Additionally, marsh yellowcress’s leaves are stipulate and its spreading fruits are oval. Creeping yellowcress is a perennial that grows in places that people have disturbed while annual marsh yellowcress can also grow in its natural habitat along shores.
Rorippa x armoracioides
A hybrid between Creeping yellowcres and Austrian yellow cress (Austrian fieldcress, R. austriaca) is known as Walthamstow yellowcress. NOT TRANSLATED YET. Meillä tavattavat ykslöt ovat todennäköisesti kulkeutuneet etelämmästä muiden kasvien mukana – myös kasvititeteellisiin puutarhoihin. Monivuotinen ja kasvullisesti lisääntyvä, kasvitieteellisissä puistoissa harmillinen puistonenätti saattaa olla hedelmällinen ja lisääntyä myös siementen kautta. Puistonenätti on hiukan kookkaampi, sen lehdet ovat ehyemmät ja lidut lyhyemmät kuin rikkanenätillä.