White milkwort

Herbs perennial, multi-stemmed, (0.5–)2–4(–5) dm, infrequently branched; caudex thickened. Stems erect, sparsely pubescent or glabrate, hairs minute, incurved. Leaves whorled at 1 or 2 nodes proximally, rarely more; sessile or subsessile; blade narrowly oblanceolate or spat­ulate proximally, to narrowly oblong or linear distally, 4–18(–25) × 1.5–2.5 mm proximally, 8–25 × 0.5–1.2(–2) mm distally, base cuneate, apex rounded to acute proximally, acute to acuminate distally, surfaces very sparsely pubescent or glabrate, hairs minute, incurved. Racemes to nearly spikes, cylindric-conic, (1–)2–8.5(–12) × 0.4–0.8 cm, often interrupted proximally; peduncle (1–)2–13 cm; bracts deciduous, lanceolate. Pedicels 0.1–1 mm, pubescent to subglabrous. Flowers white, sepals, including wings, often with greenish or purple longitudinal stripe, keel distally green or yellow, crest often purplish, 2–3.5(–4) mm; sepals ovate to oblong, 1.3–1.8 mm, pubescent; wings elliptic or ovate, 2.2–4 × 1.3–1.5(–2) mm, apex usually obtuse, rarely acute to bluntly rounded, pubescent; keel 3 mm, crest 2-parted, with 4 lobes on each side, pubescent. Capsules ovoid, ellipsoid, or oblong, 1.5–3 × 1.3–1.6 mm, margins not winged. Seeds 2–2.5 mm, pubescent; aril 0.8–1.5 mm, lobes to (1/5–)1/3–3/4 length of seed. 2n = 24, ca. 36, 52–54.

Flowering spring–summer. Grasslands, scrub, chaparral, open dry woods, open disturbed areas; 200–2000(–2600) m; Sask.; Ariz., Colo., Iowa, Kans., Mont., Nebr., N.Mex., N.Dak., Okla., S.Dak., Tex., Wyo.; Mexico (Baja California Sur, Chiapas, Chihuahua, Coahuila, Durango, Guanajuato, Jalisco, México, Nuevo León, Oaxaca, Querétaro, San Luis Potosí, Sinaloa, Sonora, Tamaulipas, Zacatecas).

Leaves of Polygala alba have abaxially embedded, linear to round, punctate glands, which are obscure in dried material but white and waxy when rehydrated.