Desmanthus illinoensis (Michx.) MacM. - Prairie Mimosa

Desmanthus illinoensis plant

Family - Fabaceae

Stems - To +/-1.5m tall, multiple from base, erect, fistulose, herbaceous, much branched, striate-nerved, glabrous or with a few sparse hairs on ridges above, green when young, becoming dark brown with age (mostly at the base).

Desmanthus illinoensis stem

Leaves - Alternate, bipinnately compound, stipulate, to 10cm long, 6-7cm broad. Stipules filiform, 5mm long. Typically 6-15 pinnae per leaf, with even number of leaflets on pinna. Small glands often at base of pinnae. Leaflets 3.5mm long, 1.5mm broad, oblique at base, linear-oblong, rounded at apex, glabrous, with strigillose margins.

Desmanthus illinoensis leaf

Inflorescence - Axillary globose pedunculate cluster of many flowers. Peduncle to +/-4cm in flower, elongating in fruit, antrorse strigose.

Flowers - Petals 5, white, to 2mm long, glabrous. Calyx tube white, 1.1mm long, 5-lobed, glabrous. Lobes 1.1mm long, glabrous, acute. Stamens 5, white, glabrous, 5mm long, well exserted. Anthers yellow, .2-.3mm in diameter. Ovary 1mm long, greenish-white, glabrous. Style 4mm long, white, glabrous, well exserted. Fruits clusters of compressed, sickle-shaped (falcate) pod to +/-2cm long, 4-5mm broad, green when fresh, becoming dark brown at maturity, with +/-6 seeds.

Desmanthus illinoensis flowers

Desmanthus illinoensis fruitsImmature fruits.

Flowering - June - August.

Habitat - Roadsides, railroads, open slopes, pastures, prairies.

Origin - Native to U.S.

Other info. - This species can be found throughout much of Missouri but seems to be absent from the northeast corner of the state as well as the central Ozark region. The plant can be identified by its small, globose clusters of many flowers and its bipinnate leaves.
If you live in extreme Southwestern Missouri you might mistake this plant for Acacia angustissima (Mill.) Ktze., except for that the latter has many more stamens per flower giving the flowers clusters a much more dense look. A. angustissima also has very dark reddish-brown, woody stems and no glands on the leaf petioles.
Desmanthus is nutritionally very important, being high in protein and fatty acids.

Photographs taken off Interstate 24 near Nashville, TN., 8-3-05.