Vascular Plants of Williamson County

Chamaecrista fasciculata var. fasciculata [Fabaceae]
partridge pea, prairie senna

Chamaecrista fasciculata var. fasciculata (Michx.) E. Greene, partridge pea, prairie senna. Annual, taprooted, unarmed, several–stemmed at base, not rosetted, erect to ascending with ascending to spreading branches, in range < 35 cm tall; shoots with only cauline leaves, exhibiting sleep movements, soft–hairy; roots not obviously nodulated.

Stems

Stems cylindric, in range to 3 mm diameter, zigzagged, tough, green, internodes typically < 15 mm long, soft hairs < 1 mm long and mostly curved.

Leaves

Leaves alternate distichous, even–1–pinnately compound, in range with 3—6 pairs of lateral leaflets spaced 3—3.5 mm apart along rachis, petiolate with pulvinus, with stipules; stipules 2, attached to petiole and stem at node, acuminate–triangular to acuminate–lanceolate, 2.5—5 × 1 mm, often with basal lobe on stem side, 3—5–veined at base, short–ciliate on margins; petiole to 6 mm long, pulvinus at base 1 mm long, with sessile nectary gland on upper side 1.5—2.5 mm from the lowest pair of leaflets and channeled above gland, the gland top–shaped with center depressed, 0.4—0.6 mm across, green, nectar–producing; rachis channeled, to 26 mm long including short extension above terminal leaflets, somewhat pilose; stipel subtending leaflet absent; petiolule = pulvinus, ± 0.7 mm long; blades of leaflets ascending from rachis, oblanceolate–oblong, 7—11 × 2.5—4.2 mm (terminal leaflets narrowly obovate, 5—10 × 1.5—4 mm), oblique at base, entire and short–ciliate on margins, obtuse with short point at tip, conspicuously pinnately veined with the strongest vein to tip and principal veins scarcely raised on lower surface, lower surface ± glaucous.

Inflorescence

Inflorescence raceme, axillary, appearing cymelike, in range 1—several–flowered, flowers helically alternate, subsessile, opening on different weeks, bracteate; pedicel ascending with pulvinus at base, at anthesis 11—20 mm long not increasing in fruit, sparsely pilose aging glabrescent, with 2 opposite or subopposite bracteoles < 5 mm from flower, bracteoles acuminate–triangular and stipulelike, 3 × 0.8 mm, 3—5–veined from base, short–ciliate on margins.

Flower

Flower bisexual, slightly bilateral, 25—30 mm across; nectary nectar–producing receptacle below ovary; sepals 5, obovate and ± boat–shaped, 15—17 × 10—12 mm, green with green–yellow to yellow on margins, sometimes red at tip, keeled, white–pilose and red–pilose along keel, short–pilose in lines and at base; petals 5, short–clawed, in bud with “banner” inside “wings,” claws ca. 2 mm long, bright yellow, limbs equal, obovate, 15—17 × 7—12 mm, bright yellow with 2–lobed (heart–shaped) red to burgundy blotch above claw, blotch ca. 3 mm wide; stamens 10, free, all appearing fertile; filaments cylindric, of different lengths, 8—11 mm long, green at base changing to yellow and orangish above midpoint; anthers basifixed, dithecal, curved inward, yellow; pollen light yellow; pistil 1, to 14 mm long, short–stalked (stipe), subsessile increasing in fruit; ovary superior, compressed fusiform, ca. 7 × 1 mm, densely villous, 1–chambered with ca. 15 ovules attached to upper side; style curved upward and tapered to tip, glabrous; stigma terminal, minute, pale yellow–green.

Fruit

Fruit legume (pod), dry, elastically dehiscent, to 12–seeded, strap–shaped, ± straight, in range to 55 × 5.5 mm, ± flat with bulges at seeds, brown with dark brown veins, obtuse at tip with short beak (style); valves twisting < 360°, like thick paper with vertical septa visible on inside wall, ± short–strigose with upward–appressed or arched hairs; stalk between pedicel and ovary to 1 mm long; bracteoles persistent in fruit.

Seed

Seed flattened–trapezoidal to flattened–rectangular, 4—4.6 × 2.5—2.8 × ± 1.2 mm, ± glossy brown, short–pointed at a corner and truncate on other end, with rows of minute, shallow pits.

A. C. Gibson