Mimosa borealis

Shrubs, erect, 0.5–2 m, usually armed, rarely unarmed. Stems terete, glabrous; prickles irreg­ular along internodes, recurved or straight; brachy­blasts present. Leaves: some 1-pinnate, with 1 or 2 pairs of leaflets; stipules subulate, 1.5–4 mm, glabrous; petiole 0.2–0.6 cm; primary rachis 0.2–0.5(–1.5) cm; pinnae 1–3(or 4) pairs; leaflets (1 or)2–7(or 8) pairs, blades obliquely oblong or elliptic to obovate, 2.5–6(–6.5) × 1–2.5 mm, margins eciliate, reticulate veins prominent abaxially, apex obtuse to acuminate, surfaces glabrous. Peduncles 0.5–1.5(–2.5) cm. Inflorescences (5–)10–30-flowered, axillary, globose or semi­globose capitula, solitary, in fascicles of 2 or 3, or in pseudo­racemes, 9–15 mm diam.; bracts spatulate, 1/3 corolla length. Pedicels 0.5–1 mm. Flowers bisexual; calyx cam­panulate, lobes 4 or 5, 1/3 corolla length; corolla purple, glabrous, lobes 4 or 5, 2/3 corolla length; stamens 8 or 10, filaments connate at bases, pink or lilac; ovary stipitate, glabrous; style attenuate at apex; stigma poriform. Legumes stipitate, curved, oblong, 15–45(–60) × 6–7.5(–10) mm, constricted between seeds, valves with (1 or)2–7(or 8) segments, bulliform, margin unarmed or randomly prickly, apex cuspidate to rostrate, faces glabrous; stipe 5–9 mm. Seeds (1 or)2–7(or 8), dark brown, lenticular, 4.5–5.5 × 3.9–4.8 × 2.5–3.5 mm, testa porous, fissural line 75%.

Phenology: Flowering Mar–Oct; fruiting Apr–Oct.
Habitat: Scrublands with Juniperus, Quercus, and associated species, rocky soils in mixed prairies, grasslands, dry rocky banks, limestone outcrops and slopes, gravelly hillsides, open areas on canyon rim.
Elevation: 100–1700 m.

Distribution

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Colo., Kans., N.Mex., Okla., Tex.

Discussion

Mimosa borealis has been found in Baca County in Colorado, Barber, Clark, and Meade counties in Kansas, and Chaves, De Baca, Eddy, Guadalupe, Harding, Lincoln, Mora, Otero, Quay, San Miguel, and Union counties in New Mexico but is more frequent in western Oklahoma, and in central, northern, and western Texas.

B. L. Turner (1959) cited Mimosa borealis as probably occurring in adjacent Mexico, but no specimens have been seen.

Selected References

None.

Lower Taxa

None.