6. Linum usitatissimum L. (common flax)

Pl. 447 g, h; Map 2023

Plants annual, Stems 25–80 cm long, solitary or more commonly several, glabrous, usually with fine longitudinal lines but not prominently ridged (circular in cross-section). Leaves alternate. Stipules absent. Leaf blades 2.5–3.0 cm long, 3–5 mm wide, linear-elliptic, narrowed or tapered to a sharply pointed tip, the margins entire. Sepals 7–9 mm long, ovate, those of both whorls with the margins thin and entire, those of the inner whorl often with minute spreading hairs. Petals 10–15 mm long, blue. Styles distinct, 2.5–5.0 mm long. Fruits usually tardily dehiscent, often remaining on the plant for some time after maturity, 7–10 mm long, 6–9 mm in diameter, ovoid to subglobose, breaking into 10 mericarps, each 1-seeded, rounded across the dorsal surface, the septa glabrous or occasionally sparsely hairy along the ventral margins, the mature fruits lacking purple stripes. Seeds 4–6 mm long, brown. 2n=30. May–September

Introduced, uncommon and sporadic, mostly in eastern and southwestern Missouri (an Old World cultigen unknown from natural populations, introduced nearly throughout North America). Roadsides, railroads, old fields, and open disturbed areas.

Common flax has an extremely long history of cultivation. It is not widely grown in Missouri, but is a common crop plant in the northern states from Minnesota to Montana. The seeds of flax are the source of linseed oil, and they are also a minor component of some animal feeds. They are also an ingredient in some bird seed mixes, which may be how some of the recently collected populations in Missouri became established. Linseed oil formerly was important as a drying agent in inks and paints, and in the manufacture of linoleum, varnishes, and soaps. Today it is no longer commonly used in human foods, but is still occasionally used in medicinal preparations. The stem fibers are used in linen cloth and sometimes also in canvas, thread, twine, paper (including cigarette rolling papers, fine writing papers, legal documents, and paper currency), and carpet material (Steyermark, 1963).