- Name also: Rough Cinquefoil, Ternate-leaved Cinquefoil
- Family: Rose Family – Rosaceae
- Growing form: Usually an annual (sometimes a short-lived perennial) herb.
- Height: 20–50 cm (8–20 in.). Sometimes with many stems. Stem (ascending–)erect, upper half branched, long-haired, sometimes reddish.
- Flower: Corolla regular (actinomorphic), yellow, approx. 1 cm (0.4 in.) broad; petals 5, usually shallowly notched, 4–5 mm (0.16–0.2 in.) long, same length as or shorter than calyx. Calyx 5-lobed, lobes initially approx. 5 mm (0.2 in.) long, in fruiting stage approx. 10 mm (0.4 in.) long; with epicalyx, epicalyx lobes narrow, almost same length as calyx lobes. Stamens 20. Gynoecium separate, pistils many. Inflorescence a corymb.
- Leaves: Alternate, basal leaves long-stalked, stem leaves stalked, stipulate. Blade with 5 leaflets, usually with 3 leaflets (central leaflet sometimes 3-lobed, leaf sometimes with 5 leaflets). Leaflets elliptic–lanceolate, large-toothed until base, both sides green. Basal leaves’ stipules narrow, sharp-tipped, stem leaves’ stipules elliptic, longer than leaf stalks.
- Fruit: Quite round, light brown, glossy, matt achene, several together.
- Habitat: Arable land, gardens, banks, wasteland, loading areas, logging clearings, sometimes shores. Rocky outcrops in Lapland.
- Flowering time: June–September.
Norwegian cinquefoil grows most commonly on sandy and gravelly waste ground and in gardens. It is principally an annual plant and is often assumed to be able to grow in any old open space, but it often grows only in one or two certain places, even though on the face of it there would be plenty other suitable habitats around. It is possible that it has difficulties spreading from one place to another.
Norwegian cinquefoil is a faithful friend of humans, but it can turn up surprisingly out in the wilds in the canyons of Kevo in Utsjoki on craggy, herbaceous rock faces and embankments. These are often south-facing, exceptionally warm places below crows’ nests. Several explanations have been advanced concerning Norwegian cinquefoil’s arrival in Lapland. Some believe that the species arrived there under its own steam from Siberia during the warm period that followed the last Ice Age, making it a native Finnish plant. Others, however, are of the opinion that it arrived recently, carried by birds from inhabited areas.
Norwegian cinquefoil grows sparsely, and as an annual that moves around from one place to the next year after year it can be found only by chance. The plants’ shoots are luckily easy enough to recognize and, with its three-lobed leaves, the overwintering rosette can actually be mistaken for strawberry (Fragaria). Norwegian cinquefoil also resembles Russian cinquefoil (P. intermedia), but the latter’s leaves have five leaflets.