Amorpha nana

Shrubs, (0.1–)0.3–0.6(–1) m; usually rhizomatous. Stems finely longitudinally grooved and ridged, gland-dotted, strigulose to glabrate. Leaves (1.5–)3–7(–10) cm; stipules linear or setaceous, (2–)3–5(–6.5) mm; petiole (2–)4–8(–10) mm, usually gland-dotted, mostly strigulose, sometimes glabrous; rachis gland-dotted, puberulent or glabrous; leaflets (7–)13–27(–41), stipels acicular, (1–)1.5–2.5(–3) mm, petiolule 0.7–1 mm, gland-dotted, especially abaxially, mostly pubescent to glabrate, blade usually elliptic to oblong or ovate, rarely obovate to suborbiculate, (2–)6–13(–18) × (2–)3–6(–8) mm, base mostly round, margins usually somewhat revolute, entire or inconspicuously crenulate, apex round to truncate or emarginate, surfaces glabrous, margins puberulent; midvein usually terminated by a slender mucro, (0.6–)0.8–1.2(–1.5) mm. Racemes unbranched, (2–)3–7(–9) cm; rachis eglandular, usually puberulent; bracteoles linear to narrowly spatulate, (2.5–)3–4(–5) mm, eglandular, puberulent. Pedicels 1–2(–2.5) mm, eglandular, usually puberulent. Flowers: calyx tube turbinate, (1.5–)1.8–2(–2.2) mm, at least distal 1/2 gland-dotted, glabrous; lobes triangular to narrowly lanceolate, (0.8–)1–2(–2.2) mm; banner dark reddish purple, broadly obcordate, 4.5–6 × 3.5–4.5 mm, distinctly clawed, margins finely erose, apex emarginate; filaments 6–8 mm, connate basally 0.5–1 mm; anthers purplish; ovary glabrous. Legumes sessile, 4.5–5.5 × 2–2.8 mm, margins curved outward abaxially, straight adaxially, at least distal 2/3 gland-dotted, glabrous. Seeds olive brown, 2.5–3 × 1–1.5 mm, reticulate. 2n = 20.

Phenology: Flowering May–Jul.
Habitat: Prairies, hillsides, buttes, sandy soils, clay soils if well-drained, in prairies, prairies on shale slopes, usually calcareous soils.
Elevation: 200–2200 m.

Man., Colo., Iowa, Kans., Minn., Nebr., N.Mex., N.Dak., Okla., S.Dak.

Discussion

Amorpha nana is listed as threatened by the state of Iowa; it is encountered more commonly in the northern and western parts of its range.

Selected References

None.

Lower Taxa