Lathyrus pusillus Elliott (singletary vetchling, tiny pea)

Pl. 398 a–c; Map 1763

Plants annual, with slender taproots, the roots not producing tubers. Stems 20–60 cm long, trailing or climbing, unbranched or few-branched from near the base, glabrous or sparsely and inconspicuously hairy, narrowly winged, the wings to 1 mm wide. Leaves with 2 leaflets, the petiole 1–2 cm long, ridged or narrowly winged, the tendrils mostly branched. Stipules 10–26 mm long, 2–6 mm wide, lanceolate to narrowly ovate, the basal lobe 7–10 mm long, lanceolate-triangular. Leaflets 2–5 cm long, 4–6 mm wide, narrowly lanceolate to narrowly elliptic or linear, angled at the base, angled or slightly tapered to a sharply pointed tip, the midvein sometimes extended into a minute sharp point at the very tip, glabrous or very sparsely hairy. Inflorescences of solitary or more commonly paired flowers, the main stalk 6–8 cm long, the flower stalks 1–4 mm long. Calyces with the tube 2.0–2.5 mm long, glabrous, the lobes 3–5 mm long, the upper 2 lobes slightly shorter than the lower 3, all lanceolate-triangular. Corollas 5–9(–12) mm long, pale lavender blue. Filaments with the fused portion 4–5 mm long, the free portion 1–2 mm long. Ovary glabrous. Fruits 2.5–4.0 cm long, 3–5 mm wide, linear to narrowly oblong, flattened, glabrous, 10–20-seeded. Seeds 1.5–2.5 mm long, more or less globose, not flattened, the surface finely wrinkled, brownish olive to dark brown. 2n=22. May–June.

Uncommon, known only from historical collections from Jasper and Newton Counties (southeastern U.S. west to Kansas and Texas; Mexico; introduced in Oregon). Chert glades; also railroads.

Lathyrus pusillus is characterized by its winged stems, small flowers, and long calyx lobes. The fruits often are borne in pairs. The tendrils are weakly developed and often unbranched.