Ononis spinosa ssp. arvensis
- Latin synonym: Ononis arvensis
- Name also: Field Restharrow, Rest-harrow
- Family: Pea Family – Fabaceae (Leguminosae)
- Growing form: Perennial herb. Rootstock short, taproot strong.
- Height: 30–80 cm (12–32 in.). Stem with long and sticky hairs, also with glandular hairs, smells unpleasant.
- Flower: Corolla zygomorphic, light red, 15–20 mm (0.6–0.8 in.) long, fused at base. Petals 5; the upstanding the ‘standard’, the lateral two the ‘wings’, the lower two united to form the ‘keel’, overall shape of corolla being butterfly-like. Keel white. Calyx 5-lobed, lobes long. Stamens 10. A single carpel. Inflorescence a lax, leafy terminal raceme or flowers axillary in pairs.
- Leaves: Alternate, stalked, stipulate. Blade with 3 leaflets, sometimes with 1 leaflet; leaflets elliptic–quite round, with serrated margin, terminal leaflet stalked. Stipules large, united with stalks.
- Fruit: Opening, same length as calyx, 6–9 mm (0.24–0.36 in.) long, 1–3-seeded pod (legume).
- Habitat: Shore-side meadows, waste ground.
- Flowering time: July–August.
- Endangerment: Vulnerable, protected in all of Finland.
Most genus Ononis plants grow close to the Mediterranean, but the number of species decreases sharply towards the north. The rare species that grow in Finland are on the border between perennial herbs and dwarf shrubs: their stems are very woody, but they usually die back to their base after the long, cold northern winter. Restharrow is the only member of its genus that has established itself in Finland, where it grows at the northern limit of its habitat in only ten islands in the archipelago in the Gulf of Finland (9 between Kirkkonummi and Sipoo and 1 near Hanko). All of the Finnish stands are in more-or-less the same kinds of places, on shingly shores that are kept quite open by breakers and ice. Further south it usually grows in dry places in different kinds of fields like inland meadows, grazing land and banks. Perhaps at its northern limit the plant only thrives in places with a lot of mineral salt in the ground, which in Finland means the sea-shore meadows, even though ground furze is not a real sea-shore species. Further south it often grows protective spines, but these are lacking in Finland. Restharrow has probably spread to Finland with traffic, probably from Estonia – this large-seeded plant could hardly have reached Finland under its own steam.
Common Restharrow & Spiny Restharrow
Ononis spinosa ssp. maritima (also Ononis repens) & Ononis spinosa ssp. spinosa (also Ononis campestris)
Nowadays (field) restharrow is classified as a subspecies, but it was previously regarded as its own species. Two other subspecies that are quite rare in the Nordic countries grow casually in Finland: these are common restharrow and spiny restharrow.