Lathyrus hirsutus L., rough pea, sinletary pea. Annual vine, tendril–bearing, taprooted, several–stemmed at base, forming lateral branches from most nodes, sprawling to ascending and climbing over other plants; shoots with leaflike, green–winged axes, every leaf tendrilar, in range appearing glabrous with sparse, inconspicuous fine hairs having swollen base (pustulate), lacking glandular hairs; tendrils = modified leaflets, 1 or 3 per leaf, if 3 paired = 2 lateral leaflets + terminal leaflet, cylindric, < 20—30 mm long, at maturity to 0.6 mm diameter, when unbranched to 22 mm long, when 3–forked lower and upper portions to 15 mm long; young roots nodulated.
Stems ridged–angled top and bottom and with 2 green (photosynthetic) wings per internode, somewhat zigzagged, internodes < 20—70 mm long, each wing 2—3.5 mm wide and decurrent from a stipule, leafy tissue sometimes glaucous, winged stems to 5—9 mm wide, each ridge descending from leaf, stems emerging from soil lacking wings and only finely 2–ridged.
Leaves helically alternate, odd–1–pinnately compound, appearing pinnately bifoliolate typically with only a basal pair of lateral leaflets and other leaflet or leaflets replaced by tendrils, petiolate without pulvinus, with stipules; stipules 2, attached to base of petiole at node, asymmetric with 1 slender lobe backward–pointing at base, principal blade ascending lanceolate, 4—8 × 1.2—2 mm, green, with inconspicuous hairs, 3–veined raised on lower surface, basal lobe acuminate, 1.5—3 mm long; petiole channeled without wings, 5—15 mm long; petiolule = pulvinus, arising from upper side of petiole, 1 mm long and < 1 mm wide, greenish, mostly glabrous; blades of leaflets oblong to narrowly elliptic, 40—90 × 7—10 mm, tapered at base and slightly cupped from stout pulvinus, entire, acute at tip, palmately veined with 3 or 5 veins arising at base and principal veins somewhat raised on lower surface, dull, not glaucous; rachis above leaflets = tendrils.
Inflorescence raceme, axillary typically from successive nodes once flowering begins, 1—3–flowered, flowers helically alternate, bracteate, sparsely pubescent with slender hairs having enlarged bases; peduncle ascending, straight, 4–sided, at anthesis to 28 × 0.6—0.65 mm and < leaf increasing to 90 mm long and often > tendril–bearing leaf in fruit, tough, green, glabrous; rachis cylindric; bractlet subtending pedicel somewhat sheathing pedicel base, awl–shaped, ca. 1 mm long, green, with several long hairs, opposite the bractlet a linear bracteole to 1 mm long; pedicel cylindric, at anthesis ca. 5 × 0.4—0.45 mm increasing 2× in fruit, pale green sometimes minutely speckled reddish, with several long hairs.
Flower bisexual, bilateral, pealike (papilionaceous), 8.5—10 mm across, lacking fragrance; nectary nectar–producing receptacle below ovary, nectar copious collected within petals; calyx 5–lobed, 7.5—8 mm long, green and somewhat glaucous, sparsely hairy; tube funnel–shaped, 3.5—4 mm long, 10–veined with raised ridges to lobes and sinuses; lobes subequal, acuminate–ovate, 3.5—4 × 1.8—2.5 mm, inner surface with subsessile glandular hairs and some long nonglandular hairs; petals 5, glabrous; banner folded forward along midline and somewhat spreading, broadly obovate, ca. 13 × 11 mm, with a stiff, flaring, thick base and roundish limb, green at base with white to midpoint, above midpoint blue to bluish purple with dark purple nectar line radiating from whitish central patch; wings 2, ± 9 mm long, clawed, claw flat and curving, 2 × 0.8 mm, colorless with a greenish midvein, limb obovate, ca. 7 × 3.5 mm, color similar to or paler than banner and without conspicuous veins, at base with backward–pointing lobe 0.5 mm long; keel of 2 petals fused from top of claw to tip along lower edge, deeply hatchet–shaped, ± 7 mm long, white, claws ca. 3 mm long, with greenish vein, limbs of keel ca. 4 × 3.5 mm, at base with a pair of backward–pointing, lobes 0.5 mm long adherent to and locked with wings; stamens 10, diadelphous (9 filaments fused and 1 free); filament sheet ± 4.5 mm long, white, free filament flattened, filament free portions cylindric and arched conforming to shape of keel, subequal, 3.5—4 mm long, white, glabrous; anthers basifixed, dithecal, monomorphic, 0.5—0.6 mm long, dull orangish yellow, longitudinally dehiscent; pollen pale orange, sticky and clumping, released in bud; pistil 1, with stigma touching anthers, sessile; ovary superior, oblong, ca. 4 × 1.5 mm long, green, sericeous with pustulate hairs upward–pointing, 1–chambered with to 6 ovules attached to upper side; style bent sharply upward from ovary, white, vertical portion cobraheadlike, lower portion cylindric and green, upper portion obovate, 2 × 1.2 mm, white with green central axis, twisted slightly so the upper surface short–strigose and the lower surface glabrous turned sideways; stigmatic on surface with hairs.
Fruit legume, dehiscent by 2 twisting valves, 2—6–seeded, oblanceolate bulging at seeds, 25—40 × 6.5—8.5 × 5.5 mm, tannish brown, straight on upper edge, conspicuously hirsute having uniformly spaced pustulate hairs with scattered subsessile glandular hairs.
Seed spheroid to subspheroid, in range 3.8—4.5 × 3.7—4 mm, dull dark brown, textured and ± cobblestonelike; hilum slitlike in elliptic scar.
A. C. Gibson