Crotalaria sagittalis L. - Rattlebox
Family - Fabaceae
Stems - To +30cm tall, erect, herbaceous, from a single large taproot, branching, densely antrorse pubescent, turning purple in strong sun, terete, single or multiple from the base.
Leaves - Alternate, short-petiolate. Petioles to 3mm long, antrorse pubescent. Blades to +7cm long, 1.5cm broad, with a single midrib, entire, blunt to acute at the apex, dull green above, grayish-green below, densely antrorse pubescent (pilose), rounded at the base. Lower leaves more elliptic than the upper.
Inflorescence - Racemes from the side of the stems in the internodes. Peduncle subtended by a large stipule which wings the stem. Stipule pubescent, colored as the leaves, tapering to the base, widest at the apex, pointed at the apices. The apices acute to acuminate, to 5-8mm long. Axis of inflorescence densely strigose. Pedicels short in flower, expanding in fruit to +7mm long, antrorse strigose. Pedicels with one linear-lanceolate bract at the base and one or two at the summit subtending the calyx. Bracts to 5-6mm long, +1mm broad.
Flowers - Corolla yellow, papilionaceous, glabrous, shorter than the calyx. Standard to +7mm broad, 7-8mm long. Wings yellow, free, to 7mm long. Keels green, connate, mostly glabrous but minutely pubescent on the basal (ventral) margin, upcurved and tapering at the apex. Stamens united into a green tube t 2.5mm long, the tube glabrous. Free portions of stamens white, +/-4mm long, glabrous. Anthers yellow, -1mm long. Style white and green, with some secund antrorse hairs, deflexed sharply. Ovary superior, glabrous, 4mm long, cylindric. Calyx accrescent, 5-lobed. Sepals subequal but the most dorsal two being the largest (to 9mm long, 2-3mm broad in flower), green, densely antrorse pubescent externally, glabrous internally, entire, with ciliate margins, linear-lanceolate to subulate. Fruits inflated, glabrous.
Flowering - May - September.
Habitat - Prairies, glades, open wooded slopes, sandy or rocky open ground, fields, railroads.
Origin - Native to U.S. and South and Central America.
Other info. - This little species can be found throughout most of Missouri but is mostly absent from the north-central portion of the state. The plant is simple to identify in the field because of its large stipules and yellow flowers. Steyermark wrote that the plant is toxic to horses.
Photographs taken at Logan Creek, Reynolds County, MO., 6-29-03.