Annual herb 15 cm - 0.8 m tall Stem: with grooved branches usually forming near the top of the plant. Leaves: mostly alternate, 1 - 3 cm long, linear, sometimes with a pair of tiny dark glands at base. Flowers: borne on an inflorescence with ascending branches, with five yellow petals 5 - 12 mm long and 2 - 4.5 mm long styles that are united for 0.3 - 1.5 mm at the base. The five sepals are 3 - 7 mm long, broad lance-shaped with a pointed tip, glandular-toothed, and persistent. Fruit: 2.5 - 3.5 mm long, egg-shaped to nearly spherical with a rounded to pointed tip, splitting into ten erect-beaked sections.
Similar species: Linum intercursum, Linum medium var. taxanum, Linum striatum, Linum sulcatum, and Linum virginianum have yellow petals and smaller fruit than the other Linum species in our region. The other four species listed above differ from L. sulcatum because they are perennials that lack gland-toothed outer sepals, united styles and a pair of glands near the leaf base. Linum sulcatum is represented by one variety in the Chicago Region. See link below for further information.
Flowering: late June to late September
Habitat and ecology: Common in dry hill prairies.
Occurence in the Chicago region: native
Etymology: Linum is the Latin name for flax. Sulcatum means furrowed.
Glabrous annual 1-3 dm, simple below, branched above into a dichasial cyme; lvs all or mostly opposite, oblong to obovate, 3-15 mm; pedicels very slender, terete, the lowest 10-25 mm, the upper shorter; sep glandular-ciliate; pet white with a yellow claw, 4-8 mm; staminodia tiny, triangular; fr ovoid-globose, 2-2.5 mm, fragile; false septa incomplete, long-ciliate; 2n=16. Native of Europe; intr. in disturbed sites from Nf. and N.S. to N.J. and Pa., w. to n. Mich. July-Sept. (L. pratense; Cathartolinum c.)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.