Broom milkwort

Herbs perennial, multi-stemmed, (0.5–)0.9–3(–5) dm, unbranched or sparsely branched distally; from thickened caudex. Stems erect, sometimes very slightly glaucous, puberulent, hairs incurved. Leaves alternate; sessile or subsessile; blade linear-lanceolate, linear, or linear-acicular, (3–)7–15 × 0.6–1.3 mm, base acute, apex acute to acuminate, surfaces subglabrous or glabrous. Racemes loosely cylindric (flowering portion may appear subcapitate from deciduous fruit), (1–)1.5–7.8 ×0.4–0.8 cm; peduncle 0.2–1 cm; bracts deciduous, ovate to lanceolate-ovate. Pedicels 0.5 mm, glabrous. Flowers white, greenish veined, wings with green or purple longitudinal stripe, keel green to purplish brown, (2.7–)2.9–4.7 mm; sepals oblong-ovate, 1.3 mm; wings spatulate-obovate, (2.4–)2.7–4.5 × 1.3–1.6 mm, apex acute to obtuse; keel 2.8 mm, crest 2-parted, with 3 usually divided lobes on each side. Capsules oblong-ellipsoid, 3–4.5 × 1.6–2 mm, abaxial locule not winged, adaxial locule slightly longer, winged, wing very narrow. Seeds 2.5–3 mm, puberulent, coat with rows of pits 0.05 mm wide; aril 1–1.9 mm, lobes (1/2–)2/3 to subequal length of seed. 2n = 32, 34.

Flowering early spring–late fall. Various substrates, mostly on limestone, open rocky areas in scrub, grasslands, disturbed areas, chaparral, open woodlands; 500–1900 m; Ariz., N.Mex., Tex.; Mexico (Chihuahua, Coahuila, Nuevo León, San Luis Potosí, Zacatecas).

Polygala scoparioides is closely related to other Mexican taxa of the Monninopsis group, such as P. mexicana Moçiño ex Cavanilles, with which it intergrades morphologically.