Orbexilum pedunculatum (Mill.) Rydb. var. pedunculatum (Sampson’s snakeroot)

Psoralea psoraloides (Walter) Cory var. eglandulosa (Elliott) Freeman

Pl. 404 a–c; Map 1787

Plants with woody taproots thickened toward the tip, not colonial, but the stems frequently 2 to several from the base, appearing clumped. Stems 25–70 cm tall, erect, green to straw-colored or light brown at the base, unbranched or less commonly few-branched above the base, moderately to densely pubescent with short, strongly upward-curved to appressed hairs toward the tip, often also inconspicuously gland-dotted, more sparsely hairy or sometimes nearly glabrous toward the base. Leaves pinnately trifoliate or those below the midpoint sometimes appearing palmately trifoliate or simple (the lowermost nodes sometimes leafless and with the stipules fused into a single scalelike structure), the petioles of well-developed leaves 0.5–5.0 cm long, the terminal leaflet with the stalk 6–10 mm long. Stipules 3–5(–8) mm long, linear to hairlike, those subtending well-developed leaves erect or ascending. Leaflets 2–7 cm long, 0.5–1.8 cm wide, narrowly elliptic to narrowly elliptic-lanceolate, those of the smaller leaves sometimes somewhat broader, the terminal leaflet similar in width but sometimes slightly longer than the lateral leaflets, rounded to bluntly pointed at the tip, the upper surface glabrous or more commonly sparsely to densely and loosely appressed-hairy, often also sparsely and inconspicuously gland-dotted, the undersurface not or only slightly lighter than the upper surface, moderately to densely hairy, not gland-dotted. Inflorescences 2–12(–20) cm long, elongating with age, the stalk 4–14 cm long, the bracts 4–7 mm long. Calyces short-hairy, the tube 1.0–1.5 mm long, the lobes 1–3 mm long, the lowermost lobe longer than the upper lobe, sharply pointed. Corollas with the banner 5–7 mm long, the wings 4.5–6.0 mm long, the keel 3–4 mm long. Filaments with the fused portion 2–3 mm long, the free portion 0.2–0.4 mm long, the anthers all similar and attached at the base. Fruits with the body 4–5 mm long, 3–4 mm wide, obliquely obovate in outline, short-tapered to a minute, strongly curved beak, the surface with a network of cross-wrinkles, but not warty, light brown to yellowish brown. Seeds 2.5–3.5 mm long. 2n=22. May–July.

Scattered in the Ozark, Ozark Border, and Unglaciated Plains Divisions; also in the northern portion of the Mississippi Lowlands (eastern [mostly southeastern] U.S. west to Kansas and Texas). Bottomland and upland prairies, savannas, bottomland and upland forests, edges of fens and sinkhole ponds, banks of streams and rivers, and tops of bluffs; also railroads and roadsides.

This species is recognized by its pinnately trifoliate leaves with narrow leaflets and suborbicular, wrinkled fruits. The inflorescences appear long-stalked with the flowers bunched near the tips.

Orbexilum pedunculatum is commonly divided into two varieties based on the size of the bracts and whether the lower surface of the leaflets, calyces, and fruits are gland-dotted or not (Isely, 1998; Grimes, 1990). However, some authors consider these taxa to represent full species (B. L. Turner, 2008). Missouri specimens lack glands on these structures and have relatively large bracts, and thus conform with var. pedunculatum, which is widespread in the central United States. 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 and has relatively small bracts.