Fabaceae, formerly named Leguminosae, the Pea family, includes over 16,000 species of trees, shrubs, climbers, and herbaceous plants worldwide. These plants are particularly valuable as crops because they do not require nitrogenous fertilizer, and even enrich the nitrogen content of the soil. The flowers are butterfly-like, with 5 unequal petals, an upright banner, a side pair of wings and 2 joined inner petals forming a keel, which envelops the stamens and pistil. There are 10 stamens, joined to a pipe, and 1 pistil. The family is characterized by the fruit, technically known as a legume or pod, which when ripe opens along both margins to release the seeds. The leaves of the Pea family bear stipules (outgrowths at the base of the leaf stalk) and are often compound, usually pinnately compound, sometimes with tendrils (thread-like outgrowths used for climbing) at the leaf tips. Another distinctive feature of the family is the presence of root nodules containing rhizobium bacteria, which fix atmospheric nitrogen, converting it into forms useful to the plant.
Guide to Identify Presented Species of the Pea Family
LEAVES WITH 3 LEAFLETS
Astragalus gilviflorus – Plains Milkvetch Plant tufted, stems 1-3 cm long. Dry, gravelly sites on the plains.
Flowers 20-30 mm long, ochroleucous. Keel purple-tipped, very short.
Leaves basal, 2-6 cm long, long-stalked, with 3 leaflets.
Medicago – Medic Annual or perennial herbs, slender. Introduced, some used for forage.
Flowers yellow or blue, many in round clusters. Seed pods curved or coiled.
Leaves alternate, divided into 3 leaflets, small-toothed, the middle one stalked.
Melilotus – Sweet-clover Tall plants, freely branched. Introduced, found mostly on disturbed ground.
Flowers small, yellow or white, sweet-smelling, in slender, spike-like clusters.
Leaves alternate, divided into 3 leaflets, sharp-toothed, the middle one stalked.
Trifolium – Clover Mostly low, slender plants, annuals or perennials, with trailing to erect stems.
Flowers white to purplish, growing numerous in dense, round heads.
Leaves are alternate, divided into usually 3 round to elongate leaflets.
LEAVES WITH 5-7 SMALL LEAFLETS. FLOWERS IN DENSE HEADS
Dalea – Prairie-clover Plants erect, 20-60 cm tall. Dry plains, slopes and foothills.
Flowers purple or white, numerous in narrow, dense spikes 2-7 cm tall.
Leaves short, odd-pinnate, with 3-9 leaflets. Stipules small, linear, bristle-like.
Lotus – Deervetch Native or introduced annual or perennial herbs with spreading to erect stems ca 10-60 cm tall. Flowers are yellow, white or cream, arranged solitary from leaf axils, or in stalked, head-like umbels. Leaves have 3 or 5 leaflets.
LEAVES PALMATELY DIVIDED INTO 5 OR MORE LARGER LEAFLETS
Lupinus – Lupine Mostly tall, robust plants with leafy, hairy stems and elongate, hairy fruit pods.
Flowers mostly numerous in tall clusters, the banner with the sides bent back.
Leaves are stalked, palmately compound of about 5-17 leaflets.
LEAVES WITH FEW TO MANY LEAFLETS AND WITH END LEAFLET
Astragalus – Milk-vetch Plants mostly with leafy stems and flat, sometimes 2-branched hairs.
Flowers whitish to purplish, in clusters, the wings longer than the blunt keel.
Leaves odd-pinnate, with usually several leaflets, and 1 leaflet at the end.
Glycyrrhiza lepidota – Wild Licorice Aromatic, glandular, sticky plant, 30-120 cm tall. Disturbed and low ground.
Flowers yellowish-white, 10-15 mm long, in several dense, stalked clusters.
Leaves odd-pinnate, with 11-19 pointed leaflets, glandular-dotted.
Hedysarum – Sweet-vetch Perennials with leafy stems. Fruits flat, with constrictions between segments.
Flowers whitish to purplish, the keel long and the wings short and lobed.
Leaves odd-pinnate, the leaflets minutely glandular-dotted, at least above.
Onobrychis viciifolia – Sainfoin Plant 20-40 cm tall. Meadows and disturbed areas, introduced.
Flowers 10-13 mm long, pinkish and lined. Wings much shorter than the keel.
Leaves on lower part of stem, odd-pinnate, with 11-17 leaflets.
Oxytropis – Locoweed Perennials with flower stalks from the base of the plant.
Flowers mostly purple or whitish, in compact clusters. The keel has a point.
Leaves basal, odd-pinnate with one leaflet at the end.
TALLER SHRUBS OR TREES
Caragana arborescens – Siberian Pea-shrub Deciduous large shrub to small tree, up to 5 m tall. Roadsides, cultivated.
Flowers yellow, about 2 cm long, 1 to 4 in bundles from leaf axils, long-stalked.
Leaves pinnately compound with 8 to 12 leaflets in pairs, without end leaflet.
Alphabetical listing with links to presented species of the Pea family:
