Vascular Plants of Williamson County

Pediomelum linearifolium [Fabaceae]
slimleaf scurfpea

Pediomelum linearifolium (Torrey & A. Gray) J. W. Grimes, slimleaf scurfpea. Perennial herb, taprooted forming enlarged root, not rosetted, 1–stemmed at base, having an open canopy with little branching, in range to 120 cm tall; shoots typically with only cauline leaves, gland–dotted (careful examination required) embedded in tissue, short–strigose.

Stems

Stems somewhat ridged, to 1.5 mm diameter except at base, with 3 slight ridges from each leaf, tough, internodes 20—60 mm long, ≥ leaf, glands mostly green so not conspicuous, short–strigose with upward–pointing hairs; lateral shoot with pulvinus at base on upper side.

Leaves

Leaves helically alternate, palmately 3–foliolate, short–petiolate with pulvinus, with stipules; stipules 2, attached to stem node and also base of petiole pulvinus, acuminate, 2.5—3.5 × < 1 mm, conspicuously gland–dotted with red glands; petiole pulvinus 1 mm long, axis above pulvinus cylindric, < 3 mm long, short–strigose with upward–pointing hairs; stipels absent; petiolule = pulvinus, 1.5—2 mm long, yellow–green; blades of leaflets subequal, linear, < 13—38 × 1.3—3 mm, somewhat folded upward from midrib, long–tapered at base, entire, acute at tip, with only midrib conspicuous and slightly raised on lower surface, upper surface inconspicuously gland–dotted and with raised minor veins, glabrous to glabrate, lower surface and margins short–strigose with upward pointing hairs.

Inflorescence

Inflorescence raceme, axillary, spreading, 10+–flowered with 2—3 flowers per node, bracteate, gland–dotted, short–strigose; peduncle cylindric, 0.5 mm diameter, green and striped, internode to 50 mm long, > internode > leaf, with purple pulvinus on upper side at base, gland–dotted between fibers; rachis to 4 nodes, to 14 × 0.2 mm, < peduncle, green, short–strigose; bract subtending set of pedicels at node, ovate, 1.5—2 mm long, green with red glands, short–ciliate on margins; bractlet subtending each pedicel obscure; pedicel lax, somewhat angled at base, 5—7 mm long, > calyx, not gland–dotted, short–strigose.

Flower

Flower bisexual, bilateral, pealike (papilionaceous), 4—5 mm across; nectary disc on receptacle surrounding pistil, green, producing abundant nectar; calyx 5–lobed, 4 mm long, purplish with conspicuous green glands; tube ± bell–shaped, ca. 2 × 2 mm, faintly 10–veined, outer surface short–strigose with upward–pointing hairs, inner surface glabrous; lobes unequal, upper 2 lobes triangular–ovate, 1.3 mm long, lateral 2 lobes 1—1.1 mm long, lower lobe ca. 1.7 mm long, lobes conspicuously white short–ciliate, short–strigose especially inner (upper) surface; petals 5; banner obovate, ca. 8.5 × 4—5 mm, lower portion somewhat clawlike = inverted triangle ca. 3 mm long, white, upper portion with not folded and with a pair of short basal lobes, below midpoint white to light pink–purple above with a set of purple radiating nectar guides 1 mm from rounded tip; wings 2, 7—7.5 mm long, < banner, clawed, claws linear, 3.5—4 mm long, white, limbs oblong with backward–point basal lobe 0.7 mm long on lower side, white at base to purple above midpoint; keel of 2 petals fused ca. 2 mm on lower side to tip, ca. 5.5 mm long, < wings, adherent but not fused to wings, clawed, claws linear, 3.5—4 mm long, white, limbs hatchet–shaped with semicircular backward–pointing basal lobe, ca. 3 × 1.5 mm, white at base to dark purple from below midpoint; stamens 10, diadelphous (9 fused and 1 free), ca. 6 mm long; filament sheet straight with short upward bend to filaments, glossy white, free portions alternating 5 with 4 shorter and scarcely visible, longer filaments somewhat ovate and 0.5—0.6 mm, white; anthers pollinating stigma in bud, dorsifixed, dithecal, 0.5—0.6 mm long, pale yellow, longitudinally dehiscent; pollen white; pistil 1, short–stalked (stipe), stalk to 0.4 mm long increasing in fruit; ovary superior, narrowly D–shaped, ca. 1.2 × 0.4 mm, yellow–green, tapered at top, glabrous and gland–dotted especially approaching top, 1–chambered with 1 ovule attached to upper side; style 4.5—5 mm long, white (greenish at base), strongly curved backward within keel with stigma surrounded by anthers; stigma capitate, hemispheroid, 0.25 mm wide.

Fruit

Fruit pod (legume), papery, indehiscent but irregularly ruptured on upper side by growth of seed, ovoid with long beak, chamber ca. 6.5 × 4 mm with inflated beak ± 3.5 mm long, light brown with many red glands.

Seed

Seed oval to somewhat kidney–shaped, ca. 6 × 4 × 2 mm, brown, hard; hilum not centered.

A. C. Gibson