3. Linum rigidum Pursh var. compactum (A. Nelson) C.M. Rogers (stiffstem yellow flax; Wyoming flax)

L. compactum A. Nelson

Pl. 446 h, i; Map 2020

Plants usually annual. Stems 8–25 cm long, several to numerous, glabrous or inconspicuously hairy toward the base, with prominent longitudinal ridges (angled in cross-section) descending from an extension of each leaf midvein. Leaves alternate. Stipules absent. Leaf blades 1.0–2.5 cm long, 1.0–1.5 mm wide, linear, narrowed or tapered to a sharp point at the tip, the margins entire or sparsely and shallowly toothed grading into glandular-toothed toward the tip. Sepals 5–9 mm long, linear-lanceolate (outer whorl) to lanceolate (inner whorl), those of both whorls with conspicuous glandular teeth along the margins and usually also with a noticeably ridged midvein. Petals 5–9 mm long; yellow. Styles fused almost to the tip, 3–4 mm long. Fruits tardily dehiscent, usually remaining on the plant for some time after maturity, 3.5–4.5 mm long, 2.6–3.4 mm in diameter, ovoid, breaking into five mericarps, each 2-seeded, more or less rounded across the dorsal surface, the septa glabrous, the mature fruits lacking purple stripes. Seeds 2.5–3.1 mm long, reddish brown. 2n=30. May–July.

Introduced, known only from Jackson County (North Dakota to Montana south to Texas and New Mexico; Canada; introduced in Missouri and Illinois). Railroads and open disturbed areas.

Although in his later treatment for the North American Flora series, C. M. Rogers (1984) treated this taxon as a separate species, most authors have continued to follow the broader concept of Linum rigidum as comprising several intergrading varieties, as C. M. Rogers (1963, 1968) proposed in his earlier taxonomic revisions of the yellow flowered flax species in North America and Central America. Steyermark (1963) and Gleason and Cronquist (1963, 1991) reported plants from Missouri as var. rigidum, which is widely distributed in the central United States and Canada (to the west of Missouri), but C. M. Rogers corrected the determination on the voucher specimens in various herbaria to var. compactum.