Plants straggling to bushy and erect. Stems glabrous. Leaf blades elliptic-lanceolate (rarely elliptic) to narrowly elliptic or linear-lanceolate, usually 2-3 cm, rarely longer, widest just below (rarely at) middle. Pedicels not reflexed in fruit (except in small, erect plants from nw North America). Flowers usually 5-6 mm diam.; sepals with midvein extending to near apex, lateral veins visible only at base, ovate to ovate-triangular, 2-3.3, to 0.5 times as long as capsule. Capsules dark brown, opaque, 3-4.5 mm, somewhat less than 2 times as long as broad. Seeds smooth or indistinctly rugulose. 2n = 52.
Flowering spring-summer. Open marshy woodlands and grasslands, river and roadside gravel, among boulders on talus slopes, edges of moist lowland and floodplain forests; 0-3500 m; Greenland; St. Pierre and Miquelon; Alta., B.C., Man., N.B., Nfld. and Labr., N.W.T., N.S., Nunavut, Ont., P.E.I., Que., Sask., Yukon; Alaska, Calif., Colo., Conn., Idaho, Maine, Mass., Mich., Minn., Mont., Nev., N.H., N.J., N.Y., Oreg., Pa., R.I., Utah, Vt., Wash., W.Va., Wis., Wyo.; Europe; Asia.
The circumboreal subsp. borealis is highly variable in habit, leaf shape, and inflorescence development. This variation is partly genetic but is also greatly influenced by the environment. The broad-leaved form named Stellaria calycantha var. latifolia is of occasional occurrence. A similar broad-leaved form occurs in subsp. sitchana. In both of these variants, the leaf blades are elliptic-lanceolate to elliptic, with a length-to-width ratio of 2.5-3 : 1. These variants retain their characters under cultivation. However, the occurrence of the same variational trend in both subspecies makes taxonomic recognition of this variation problematic.
Subspecies borealis hybridizes fairly frequently with S. longifolia to produce a sterile triploid (2n = 39). These hybrids are intermediate between the parents but have copious inflorescences with widely divaricate branches and numerous small, completely sterile flowers. Similar hybrids can be readily produced experimentally (C. C. Chinnappa 1985). European and North American workers (most recently B. Jonsell and T. Karlsson 2000+, vol. 2) often have called these hybrids S. alpestris Fries, but that name has caused a great deal of confusion and R. K. Rabeler (1986) concluded that it more correctly applies to subsp. borealis.
