Vascular Plants of Williamson County

Linum usitatissimum [Linaceae]
common flax, cultivate flax

Linum usitatissimum L., common flax, cultivate flax. Annual, taprooted, not rosetted, 1(—2)–stemmed at base, typically unbranched to above midplant with ascending flowering branches in canopy, in range to 75 cm long; shoots with only ascending cauline leaves, glabrous and somewhat glaucous.

Stems

Stems cylindric, to 10 mm diameter, tough, green portion minutely spotted (stomates), forming periderm at base on lower portion.

Leaves

Leaves helically alternate (sometimes appearing whorled on the lowermost stem), simple and sessile, without stipules; blade ± narrowly lanceolate, in range 15—28 × 2.6—3.5 mm, minutely toothed to subetire on margins, acuminate–acute at tip, 3–veined at base with veins parallel and slightly raised on lower surface.

Inflorescence

Inflorescence leafy monochasial cyme, terminal, open, many–flowered, bracteate, glabrous; peduncle = upper portion of stem; primary canopy branches to 200 mm long; axes slender and wiry, to 1 mm diameter, tough; bractlet subtending pedicel leaflike, sessile; pedicel at anthesis to 9 mm long increasing to 4× and suberect in fruit, somewhat ridged.

Flower

Flower bisexual, radial, 17—23 mm across; receptacle minutely hard–papillate on outer surface; sepals 5, overlapping and strongly attached to receptacle, ovate with short–acuminate tip, outer 3 sepals at anthesis 6.5—7 × 2.5 mm, 5–veined at base, green with narrow colorless margins to above midpoint, with midvein raised on back, tip often appearing cylindric because inrolled adherent with minute teeth, purplish at tip, inner sepals at anthesis 7.5—8 × 3 mm, green with wide colorless margins nearly to tip conspicuously short–ciliate and fringed; petals 5, attached to rim of staminal cup, fan–shaped, 10—13(—15) × 7.5—9 mm, blue with ca. 7 veins, violet, radiating veins from base, basal portion white and narrowly margined with midrib raised on upper side, pigmented limb with principal veins slightly raised on lower surface, glabrous, easily abscised; stamens 5, fused at bases into a short tube; tube surrounding base of ovary 0.5 mm long, white; filaments erect, narrowly triangular, 1—1.2 mm long, white to midpoint and light violet above midpoint; anthers dorsifixed, dithecal, 1.8—2 mm long, white or basal portion tinged pale violet, longitudinally dehiscent; pollen colorless; pistil 1, 4—5 mm long; ovary superior, ovoid, ca. 2 × 1.5 mm, glossy green, 5–chambered, each chamber with 2 ovules; styles 5, fused only at base, at anthesis 2—2.5 mm long, white or slightly enlarged stigmatic portion tinged pale violet.

Fruit

Fruit capsule splitting into 5 2–seeded mericarps, septicidal and loculicidal, 10–seeded, broadly ovoid to subspheroid, in range ca. 6—7 × 6.5—7.5 mm, pointed at tip, glossy, glabrous.

Seed

Seed ovate in outline strongly compressed side–to–side, 4.5—5 × 2.5 mm, glossy brown.

A. C. Gibson