Perennial (rarely annual) herb 20 cm - 1 m tall Stem: unbranched below inflorescence. Leaves: opposite near base, becoming alternate above, with 30 to 150 below the inflorescence, 1 - 2.5 cm long, 1.5 - 3.5 mm wide, gradually becoming smaller above, linear to lance-shaped or lance-elliptic with pointed awl-shaped tips. Flowers: borne on an inflorescence with stiffly ascending-spreading and elongate branches, with five yellow petals 4 - 8 mm long. The five sepals are lance-shaped with a pointed tip, with the outer sepals 2 - 5 mm long and toothless and the inner sepals shorter and gland-toothed. Fruit: a more or less persistent capsule, 2 mm across, depressed-spherical, splitting into five or ten 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. Linum intercursum has a narrow-tipped capsule, L. striatum has a prominently ridged stem and an elongate inflorescence, and L. virginianum has slender ascending inflorescence branches and a leaf base that continues down the stem but does not form a strong ridge.
Flowering: mid June to early October
Habitat and ecology: Calcareous pond shores near Lake Michigan or areas in which sand was artificially removed down to the water table.
Occurence in the Chicago region: native
Etymology: Linum is the Latin name for flax. Medium means intermediate. Texanum means "from Texas."
Author: The Morton Arboretum
From Flora of Indiana (1940) by Charles C. Deam
In southern Indiana this plant has been found on washed slopes in fallow fields, on post oak ridges, and in moist, hard clay soil on post oak flats. In the northern part of the state it is found in the prairies and lake areas in moist, sandy soil, usually associated with Cladium mariscoides, Juncus torreyi, Liatris spicata, etc. Rare. My [Deam] specimens no. 41481 from Brown County may belong to the typical form. They are rather small and I hesitate to refer them to the typical form for fear they are only extremes of the variety.