Flora of Oregon

Herbs annual or perennial.

Stems prostrate to erect, generally pubescent.

Leaves alternate, pinnate or sub-palmate; leaflets 3, margins toothed distally, tips mucronate or mucronulate, surfaces glabrous or pubescent; petioles present; stipules present, adnate to petioles, entire to lacerate.

Inflorescences 1–30-flowered axillary racemes, sometimes umbellate or sub-capitate.

Flowers papilionaceous; calyces radial or bilateral, campanulate, fused, lobes 5; corollas petals 5, often ephemeral, free, yellow, violet, or variegated yellow-violet, keels obtuse or rounded; stamens 10, diadelphous; styles short, glabrous.

Fruits indehiscent, becoming exserted, generally spiraled in 2–6 turns and forming burs, sometimes reniform or rarely sickle-shaped, spiny or unarmed.

Seeds 1–several, reniform or sometimes oval.

Worldwide. ~87 species; 6 species treated in Flora.

All of Oregon’s Medicago species are introduced. These include several widely established species that are cultivated for forage or used for soil improvement due to their symbiotic associations with nitrogen-fixing bacteria. Alfalfa (M. sativa) is perhaps the most important forage plant in the temperate world. Two taxa (M. falcata and M. turbinata) have been collected only once or twice and do not appear to be established in our flora. Medicago falcata, yellow-flowered alfalfa, is a recent waif with yellow corollas and straight or falcate fruit, which distinguish this species from all other Medicago found in Oregon. Medicago turbinata, southern medic, has been collected only twice over a century ago on ballast. Fruit measurements include the length of the spines.