Perennial herb 20 cm - 0.8 m tall Stem: unbranched below the inflorescence or with few branches at the base. Leaves: opposite near base, becoming alternate above, with fifteen to 60 below the inflorescence, 0.8 - 2.5 cm long, 1 - 6 mm wide, narrow elliptic to narrow and inversely egg-shaped. Flowers: borne on an inflorescence with stiffly ascending slender branches, with five yellow petals 4 - 7 mm long. The five sepals are 2 - 3 mm long, lance-shaped with a pointed tip, with the outer sepals slightly longer and the inner sepals sparsely gland-toothed. Fruit: a capsule, 1.5 - 3 mm long, egg-shaped with a pointed tip, splitting into ten sharply pointed segments.
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. Linum sulcatum is an annual with gland-toothed outer and inner sepals, styles that are united near the base, and leaves with a pair of glands at the base. The other three species have depressed-spherical fruit. In addition, L. medium var. taxanum has 30 to 150 leaves below the inflorescence, L. striatum has a prominently ridged stem, and L. virginianum has a leaf base that continues down the stem but does not form a strong ridge.
Flowering: late July to mid August
Habitat and ecology: Rare in sandy soil.
Occurence in the Chicago region: native
Etymology: Linum is the Latin name for flax. Intercursum means "running between."
Author: The Morton Arboretum
From Flora of Indiana (1940) by Charles C. Deam
Moist, sandy soil on the borders of marshes in black oak woods. Rare.
Glabrous perennial 2-8 dm, simple below the infl or few-branched at base; lvs mostly 25-50 below the infl, narrowly elliptic to oblanceolate, 1-2.5 cm נ1.5-5 mm, opposite below, usually alternate above; infl of slender, rather stiffly ascending-spreading branches; pedicels 1-4 mm; sep lanceolate, acute, 2-3 mm, the inner usually (and the outer seldom) sparsely glandular-toothed; pet yellow, 4-7 mm; fr turbinate, ±pointed, 2-3 mm, readily dehiscing into 10 sharp- pointed mericarps; exposed portion of the fr anthocyanic; false septa evidently incomplete, glabrous; septa sparsely but evidently ciliate; 2n=36. Open oak or pine woods and open places on the coastal plain from e. Mass. to N.C., thence inland to Tenn. and Ala.; isolated in nw. Ind. June, July. (Cathartolinum i.)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.