Annual herb with a taproot 10 - 30 cm tall Stem: upright to ascending or decumbent, slender, much branched at base, sometimes minutely glandular-hairy. Leaves: opposite, stalkless, 0.5 - 2 cm long, 0.5 - 1 mm wide, linear to thread-shaped with a blunt to pointed tip, prominently one-veined, fleshy. Inflorescence: an open, hairy-branched cluster (cyme) of five to thirty flowers on a 1.5 - 3 cm long stalk. Flowers: white. Stalk 0.3 - 3 cm long, glandular-hairy. Stamens ten. Styles three. Sepals: five, 4.5 - 6 mm long, lance-shaped with a pointed tip, prominently three- to five-veined, sometimes sparsely glandular-hairy. Petals: five, white, 5 - 8 mm long, reverse egg-shaped with a rounded tip, broadly notched. Fruit: a dehiscent capsule (opening by six teeth), short-stalked, 3 - 4 mm long, equal to or shorter than the sepals, narrowly ellipsoid. Seeds reddish brown to black.
Similar species: The linear to thread-shaped leaves (usually under 2 mm wide) help distinguish this species and Arenaria stricta from all other Arenaria in the Chicago Region. Arenaria stricta differs by having mostly flat, linear to bristle-like leaves and hairless inflorescence branches.
Flowering: May to early July
Habitat and ecology: Very local to sometimes abundant, especially where limestone beds are near the surface of the ground.
Occurence in the Chicago region: native
Etymology: Arenaria comes from the Latin word arena, meaning sand, referring to the fact that most species in this genus prefer sandy habitats. Patula means spreading.
Annual, usually much-branched at base, glabrous or minutely glandular- puberulent; stems slender, 1-2 dm, decumbent or erect; lvs mostly cauline, several pairs, 1-2 cm נ0.5-1 mm; infl open, often extending to below the middle; pedicels 15-30 mm; sep 4.5-6 mm, narrowly lanceolate, acute; pet white, 5-8 mm; fr equaling or shorter than the sep, lance-oblong, the 3 valves dehiscent to the middle; seeds gray-brown, low-tuberculate. Apr.-June. (Minuartia p.) Var. patula, occurring in rocky soil, barrens, and meadows, from Ind. and Minn. to Va., Ala., and Tex., has 5-nerved sep, and the seeds are 0.5-0.7 mm. Var. robusta (Steyerm.) Maguire, occurring on limestone slopes in Mo., Ky., and Tenn., has 3-nerved sep, and the seeds are 0.7-0.9 mm.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.