34. Linum rigidum Pursh, Fl. Amer. Sept. 1: 210. 1813.
Stiffstem flax Stiffstem flax
Herbs, annual, 15–50 cm, glabrous throughout or puberulent near base of stem. Stems erect, branches few, fastigiate or spreading-ascending. Leaves alternate, erect; stipular glands present or absent; blade linear, 11–30 × 0.7–1.6 mm, margins entire or distally sparsely toothed, not ciliate, apex acute. Inflorescences panicles or cymes. Pedicels 4.5–9 mm. Flowers: sepals deciduous, lanceolate to broadly lanceolate, 5.5–9.5 mm, margins of inner sepals conspicuously scarious, all conspicuously glandular-toothed, apex sharply acute to acuminate; petals coppery yellow or orange, red-lined or with short pale to deep brown-red zone at base, obovate with short claw, 6–18 mm; stamens 6–8 mm; anthers 1–1.8(–2.3) mm; staminodia absent; styles connate nearly to apex, 3–11 mm; stigmas pale, capitate. Capsules ellipsoid, 3.5–4.5 × 2.6–3.4 mm, apex obtuse, dehiscing into 5, 2-seeded segments, segments blunt or subacute, persistent on plant, false septa complete, proximal part membranaceous, not terminating in loose fringe, distal part cartilaginous, margins not ciliate. Seeds 2.6–3.6 × 0.9–1.2 mm. 2n = 30.
Varieties 2 (2 in the flora): w, c North America, n Mexico.
The corollas of Linum rigidum are funnelform at the base, opening out into a broader bowl. The styles and stamens are yellow, although the distinct portion of the style may be slightly maroon; the stigmas are grayish or light green. The stems of L. rigidum are angled. Its capsule walls are so thin that the dark seeds can be seen through them. C. M. Rogers (1984) noted that L. australe, L. berlandieri, L. compactum, and both varieties of L. rigidum are closely related, and that there is some overlap in character expressions, not easily resolved in a dichotomous key.