Synonyms: Lotus corniculatus var. arvensis, Lotus tenuis
Bird's-foot trefoil is a weedy perennial species with numerous prostrate to ascending stems up to 50 cm long. When trailing across the ground, the stems will root at the node. Plants are typically glabrous but may bear some spreading hairs on the stems and in the inflorescence. The sessile leaves are alternate along the stems with 5 leaflets (See photo.). The basal pair of leaflets are short petiolate and stipule-like in appearance, but are similar in size and shape to the distal trio of leaflets. The blades of the leaflets are elliptic to obovate in shape and measure 5-17 mm long and 2-7 mm wide with minutely toothed.
The flowers are in umbel-like, axillary clusters of 3-15 flowers each. The peduncles are 3-12 cm long and bear a ternate (3 leaflet) bract directly beneath the umbel. The yellowish flowers are 8-15 mm long and bear red stripes on the erect banner and may turn reddish with age. The banner is positioned well back in relation to the wings and keel, while the wings are much longer than the keel. The calyx is 5-8 mm long with narrowly-linear teeth about equal in length to the tube. The narrow pods are 20-40 mm long and 2-3 mm wide. They self-seed readily, thus allowing the species to spread easily in disturbed habitats.
I have to admit using this species in the front of the flower beds in my garden. The flower heads add color to the bed and the leaves are fairly interesting. I try to keep the spreading stems clipped to provide for a bushy growth, but if left to its own, the stems as mentioned above do root at the nodes and it reseeds easily so can become tough to remove when it starts crowding out other desired species!
A weedy species, bird's-foot trefoil is commonly found in disturbed places such as roadsides, rock and gravel quarrys, fallow fields and waste areas.
A European species, bird's-foot trefoil is commonly found west of the Cascades in Washington and Oregon, although it is locally found eastward to Idaho.
In the Columbia River Gorge it may be found between the elevations of 100'-2100' from the Sandy River eastwards to near the Deschutes River.