Lathyrus venosus Muhl. ex Willd. (bushy vetchling)

L. venosus var. intonsus Butters & H. St. John

Pl. 398 l, m; Map 1766

Plants perennial, with rhizomes, the roots not producing tubers. Stems 40–120 cm long, trailing or climbing, usually branched, sparsely to densely and finely hairy, angled but not winged. Leaves with (6)8–14 leaflets, the petiole 0.5–1.0 cm long, unwinged, the tendrils branched or unbranched. Stipules 4–10(–20) mm long, 1–4 mm wide, narrowly lanceolate to lanceolate, the basal lobe 1–6(–14) mm long, narrowly lanceolate to oblong-lanceolate. Leaflets 3–6 cm long, 10–30 mm wide, narrowly to broadly elliptic or oblong-lanceolate, rounded to angled or broadly angled at the base, angled to a usually bluntly pointed tip, the midvein sometimes extended into a minute sharp point at the very tip, finely hairy, at least on the pale undersurface. Inflorescences dense racemes of 8–20 flowers, the stalk 6–12 cm long, the flower stalks 3–5 mm long. Calyces with the tube 3.5–5.0 mm long, finely hairy, the lobes 1.0–4.5 mm long, the upper 2 short and triangular to broadly triangular, the lowermost lobe 2–3 times as long as the upper 2, narrowly triangular, the lateral lobes of the lower lip intermediate in size and shape. Corollas 12–20 mm long, pinkish purple, to lavender, occasionally somewhat bicolorous (the wings and keel lighter than the banner). Filaments with the fused portion 9–10 mm long, the free portion 4–5 mm long. Ovary glabrous. Fruits 4–6 cm long, 5–8 mm wide, linear to narrowly oblong, flattened, glabrous, 5–10-seeded. Seeds 4–5 mm long, more or less oblong in outline, slightly flattened, the surface smooth, reddish brown to dark brown. 2n=28. May–June.

Uncommon in the Ozark Division; also known from a single historical collection from the city of St. Louis (eastern U.S. west to North Dakota and New Mexico, Alaska; Canada). Mesic to dry upland forests, margins of lakes, and ledges and tops of bluffs; also roadsides.

Lathyrus venosus is recognized by its bushy habit, leaves with 6–10 relatively large and usually finely hairy leaflets, relatively weakly developed tendrils, and hairy calyces. It tends to grow in drier habitats than does the morphologically similar L. palustris. Several infraspecific taxa have been recognized based on differences in pubescence (Hitchcock, 1952; Steyermark, 1963). The var. venosus, which is glabrous or nearly so, occurs to the east of Missouri. Missouri collections are at least sparsely hairy on the stems and foliage and correspond to var. intonsus. However, Isely (1998) concluded that the varieties are difficult to separate in many areas and thus abandoned their recognition.

Steyermark (1963) noted that this species sometimes occurs as relatively extensive colonies with few or no flowering stems. Thus, it is possible that the taxon has been undercollected in the state.