Lesser Hop Trefoil
- Name also: Lesser Trefoil, Suckling Clover, Yellow Shamrock
- Family: Pea Family – Fabaceae (Leguminosae)
- Growing form: Annual herb.
- Height: 5–20 cm (2–8 in.). Stem limp–ascending, thin, sparsely haired.
- Flower: Corolla irregular (zygomorphic), pale yellow, finally yellowish brown, 3–4 mm (0.12–0.16 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.); standard unwrinkled, wings parallel with keel. Calyx 5-lobed. Stamens 10. A single carpel. Inflorescence long-stalked, a quite lax, 3–15-flowered raceme.
- Leaves: Alternate, stalked, stipulate. Blade with 3 leaflets; leaflets spatulate, with entire–slightly curved margins, central lobe stalked. Stipules mostly fused with stalk, approx. same length as leaf stalk.
- Fruit: Indehiscent pod, remains inside calyx.
- Habitat: Harbours, wasteland, lawns.
- Flowering time: June–July.
Genus Clover is the largest in the Pea family with almost 300 species. Most of these grow in the temperate regions of the northern hemisphere; on the other hand there are also a large number of annual species that grow in subtropical regions. Lesser hop trefoil is already quite a common sight in southern Scandinavian lawns and yards. It has arrived in Finland at least in the ballast soil in sailing boats, in German soldiers’ provisions, among crop seeds and mixed in with vegetable roots. Most often it has remained casual and it has only managed to establish itself on the Åland Islands. It may simply be that the Finnish climate is too harsh on the mainland, because with its limp stem and low height it would be expected to be able to grow to at least some extent on cultivated lawns and other areas where people influence the environment.
Hop trefoil (T. campestre) is a slightly more common clover with small yellow flowers that is difficult to tell apart from lesser hop trefoil. Hop trefoil’s inflorescence is however larger (10–30-flowered), its corolla is darker and its standard is clearly crinkled. Large hop trefoil (T. aureum) can usually be told apart from lesser hop trefoil through its size; despite its diminutive dimensions the stipules on lesser hop trefoil’s leaves are larger. Additionally, lesser hop trefoil’s terminal leaflet is stalked (large hop trefoil’s is stalkless).