Stylosanthes biflora (L.) Britton, Stearns & Poggenb. (pencil flower)

S. biflora var. hispidissima (Michx.) Pollard & C.R. Ball

S. riparia Kearney

Pl. 408 k–m; Map 1807

Plants perennial herbs, with a long, stout taproot below an often branched, woody caudex. Stems 10–40(–60) cm long, wiry, ascending to more commonly spreading, usually well-branched, sometimes forming loose mats, unarmed, glabrous or more commonly moderately to densely pubescent with fine, appressed-ascending hairs and often also stiff, bristly, spreading hairs. Leaves pinnately trifoliate, the petiole with the free portion 1–3 mm long, the basal half fused to the stipules. Stipules fused to the petiole and into a sheath around the stem, this 4–7 mm long, hairy, the free portions 3–6 mm long, linear, bristly-hairy along the margins; stipels absent. Leaflets 8–20(–40) mm long, 3–7(–18) mm wide, the terminal leaflet sometimes slightly larger than the lateral pair and with a stalk 1–2 mm long, narrowly elliptic to lanceolate, oblanceolate, or rarely narrowly ovate, angled at the base, angled or slightly tapered to a bluntly or sharply pointed tip, the midvein extended into a minute sharp point at the very tip, the margins entire, glabrous or sometimes sparsely bristly-hairy, the surfaces glabrous, the upward-angled lateral veins relatively prominent on the undersurface. Inflorescences axillary and terminal, of solitary flowers and/or short, dense spikelike clusters of 2(–4) flowers, the stalk 4–8 mm long, hidden in the stipular sheath (the inflorescences thus appearing sessile or nearly so), the bracts 3–5 mm long, 1–3 mm wide, linear to narrowly lanceolate, sometimes 3-lobed, usually bristly-hairy; bractlets 2–3 mm long, linear. Flowers sessile, but sometimes appearing short-stalked because of a hypanthium below the perianth, this 3–5 mm long, usually glabrous. Calyces (above the hypanthium) with the tube 2–3 mm long, bell-shaped, glabrous, 2-lipped, the upper 2 lobes 1.2–1.8 mm long, fused to about the midpoint, the free portions narrowly ovate-triangular, the lower lip with the lateral lobes similar in length to the upper ones, the lowermost lobe 2–3 mm long, narrowly oblong-triangular, its margins sometimes spreading-hairy. Corollas papilionaceous, orangish yellow to yellow, often fading to whitish or pinkish, the banner 5–9 mm long, 4–7 mm wide, the expanded portion broadly obovate to nearly circular, rounded to more commonly slightly and broadly notched at the tip, slightly keeled longitudinally, bent upward abruptly toward the base, the wings 3.5–5.0 mm long, 2–3 mm wide, oblong-oblanceolate, rounded at the tips, somewhat cupped around the keel, the keel 3–5 mm long, 2–3 mm wide, boat-shaped, curved upward, bluntly pointed at the tip. Stamens 10, the filaments all fused into a tube 5–6 mm long, the free portions 2–3 mm long, curved, the anthers of two kinds, 5 of them oblong and attached toward the midpoint, alternating with 5 that are nearly globose and attached near the base, yellow to orange. Ovary 1–2 mm long, usually minutely hairy, the style 6–8 mm long, glabrous or minutely hairy, curved or curled, the stigma terminal, minute. Fruits loments, 5–7 mm long, 2–3 mm wide, divided into 2 segments, the lower segment usually infertile, appearing stalklike, pale, and hairy, the upper segment 3.0–4.5 mm long, obliquely ovate in outline, flattened, tapered at the tip to a curved or curled beak 0.5–1.0 mm long, the outer wall papery, brownish yellow to brown, glabrous or minutely hairy, with a prominent network of rounded ridges (sometimes appearing wrinkled), indehiscent, shed as a unit, 1-seeded. Seeds 2.0–2.5 mm long, broadly oblong-circular in outline, flattened, the surface yellowish brown to brown, with irregular, blunt ridges, somewhat shiny. 2n=20. June–September.

Scattered nearly throughout the state, but apparently absent from the northern half of the Unglaciated Plains Division and the western half of the Glaciated Plains (eastern U.S. west to Kansas, Texas, and possibly Arizona). Glades, upland prairies, sand prairies, savannas, dry upland forests, tops of bluffs, banks of streams and rivers, and rarely margins of ponds; also strip mines, old fields, and roadsides.

Stylosanthes biflora is recognized by the wiry stems with long, bristly hairs, orangish yellow flowers, and fruits that are 1-seeded loments. It is fairly uniform throughout its wide range, with only minor variation in leaf shape and habit (Mohlenbrock, 1957). Several species of Stylosanthes are important forage plants in the tropics.