Orbexilum pedunculatum

Sampson's Snakeroot

Orbexilum pedunculatum plant

Family - Fabaceae

Stems - To +/-50cm tall, multiple from base, from creeping rhizomes (roots with small nodules), erect to ascending, herbaceous, angled, striate, antrorse strigose (especially on the striations).

Orbexilum pedunculatum stemStem and stipule.

Leaves - Alternate, trifoliolate, petiolate, stipulate. Stipules subulate, to 7-8mm long, 2mm broad at the base, antrorse strigose externally and ciliate-margined, glabrous internally, with parallel nerves. Petioles with an adaxial groove, antrorse strigose (sometimes sparse), to +/-7cm long, reduced upward. Petiolules to 6mm long (terminal) 1mm long (lateral), densely pubescent. Leaflets of the lower leaves notched at the apex, oblong-elliptic to narrowly oblanceolate, entire, 3-4cm long, +/-1.5cm broad. Leaflets of the upper leaves lance-linear to oblong-linear, entire, to +/-8cm long, +/-1.2cm broad. All leaflets strigose.

Orbexilum pedunculatum leaf

Orbexilum pedunculatum leaves

Inflorescence - Axillary pedunculate racemes to +/-4cm long (tall), elongating slightly in fruit. Peduncles to +/-11cm long, antrorse strigose. Pedicels to -2mm long, antrorse strigose. Flowers 1-4 at a node.

Orbexilum pedunculatum inflorescence

Flowers - Corolla lilac (drying tan), papilionaceous. Standard 6mm long, 5mm broad, glabrous, with a darker purple splotch near the base or just a darker purple midvein. Wings and keels basally connate. Keels short, deep purple at the apex, 2.5-3mm long. Wings spreading. Stamens diadelphous, the tube white and glabrous, to 3mm long. Anthers yellow, .1-.2mm long. Ovary green, glabrous, 1.1mm long, with one ovule. Style translucent, 2-3mm long. Calyx 5-lobed (weakly bilabiate), antrorse pubescent, the tube to -1mm long. Lobes acute, the largest to 3mm long. All calyx lobes ciliate-margined, glabrous internally.

Orbexilum pedunculatum flowersFlowers close-up.

Flowering - May - July.

Habitat - On acid soils. Open rocky woods, glades, prairies.

Origin - Native to U.S.

Other info. - This attractive bean can be found mainly in the Ozark region of Missouri. The plant is easy to identify because of its lilac flowers, long-stalked terminal leaflets, thin leaflets, and antrorse strigose stems.
This species requires acidic soil but would make a fine garden subject if the right conditions were provided.

Missouri's plants are assignable to var. pedunculatum. The other taxon, known variously as var. gracile (Torr. & A. Gray) J.W. Grimes or O. gracile (Torr. & A. Gray) Rydb., occurs mainly along the Atlantic Coastal Plain from Virginia to Florida. It is gland-dotted on the calyces, fruits, and leaf undersides, and has relatively small bracts.

Photographs taken on Bear Mountian, MO., 6-1-03.