Twin-flower sandwort, alpine stitchwort

Alsinopsis obtusiloba Rydberg, Bull. Torrey Bot. Club 33: 140. 1906, based on Arenaria obtusa Torrey, Ann. Lyceum Nat. Hist. New York 2: 170. 1827, not Allioni 1785; A. obtusiloba (Rydberg) Fernald; Lidia obtusiloba (Rydberg) Á. Löve & D. Löve

Plants perennial, cespitose to mat-forming. Taproots stout, woody. Stems erect, green, 1-12 cm, trailing stems 2-20+ cm, stipitate-glandular, internodes of flowering stems 1-6 times as long as leaves. Leaves tightly overlapping (vegetative), variably spaced (cauline), usually connate proximally, with tight, scarious to herbaceous sheath 0.3-1.5 mm; blade straight to outwardly curved, green, 3-angled, 3-veined abaxially, midrib prominent, lateral veins weak in distal 3, needlelike to subulate, 1-8 × 0.4-1 mm, flexuous, margins not thickened, herbaceous, sometimes finely ciliate, apex green, rounded to acute, often apiculate, somewhat navicular, shiny, glabrous; axillary leaves present among vegetative leaves. Inflorescences solitary flowers, terminal, or occasionally in 2-3-flowered, open cymes; bracts subulate, herbaceous. Pedicels 0.3-1.5 cm, stipitate-glandular. Flowers: hypanthium cup-shaped; sepals prominently 3-veined proximally, narrowly ovate to oblong (herbaceous portion lanceolate to oblong), 2.9-6.5 mm, not enlarging in fruit, apex often purple, narrowly rounded, hooded; petals ovate to spatulate, 1.2-2 times as long as sepals, apex rounded, entire. Capsules narrowly ellipsoid, 3.5-6 mm, equaling sepals. Seeds reddish tan, suborbiculate with radicle prolonged into beak, somewhat compressed, 0.6-0.7 mm, obscurely sculptured (50×). 2n = 26, ca. 52, 78.

Flowering summer. Dwarf willow communities, fell-fields, snow beds in subalpine and alpine areas; 0-4000 m; Alta., B.C., N.W.T., Yukon; Alaska, Ariz., Calif., Colo., Idaho, Mont., Nev., N.Mex., Oreg., Utah, Wash., Wyo.; Asia (Russian Far East).

Minuartia obtusiloba, an amphi-Beringian species, sometimes forms hybrid swarms with M. arctica. Specimens labeled Arenaria sajanensis Willdenow ex Schlechtendal from western North America, sometimes referred to M. biflora (e.g., H. J. Scoggan 1978-1979, part 3), are likely to be M. obtusiloba.