Sonoran or Santa Catalina Mountain centaury

Erythraea nudicaulis Engelmann, Proc. Amer. Acad. Arts 17: 222. 1882; Centaurium nudicaule (Engelmann) B. L. Robinson

Herbs annual, 4–27 cm. Stems 1–several, usually simple or branching only above middle. Leaves: basal often present at flowering; blade elliptic to obovate, 3–26 × 2–10 mm, apex obtuse to acute; cauline blades elliptic-oblong to lanceolate or rarely ovate, (proximal, sometimes extending distally into inflorescence) to narrowly linear or filiform (distal), 3–31 × 0.7–6 mm (distal leaves usually 1–2 mm wide, occasionally to 4 mm), apex subacute to acuminate. Inflorescences diffuse, proximally dichasial, distally monochasial or completely monochasial cymes; pedicels (8–)15–75 mm. Flowers 5-merous; calyx 4–8 mm; corolla scarcely constricted above ovary, 6.5–10(–12.5) mm, lobes lanceolate, 2.5–4.5 × 0.5–3 mm, apex obtuse; stigmas 2, fan-shaped. Seeds reddish brown. 2n = 42 (Mexico).

Flowering winter–spring. Stream banks in open woods, wet meadows; 900–1500 m; Ariz., N.Mex., Tex.; Mexico (Sonora).

Zeltnera nudicaulis is the only species of this genus in the flora area in which the corolla is not distinctly constricted above the ovary, and it has leaves thicker than those of the other Zeltnera species with which it is sympatric. It differs distinctly from Z. exaltata in its widely separated cauline leaves, which contrast with its much wider basal and near-basal leaves.