1. Silene acaulis (Linnaeus) Jacquin, Enum. Stirp. Vindob. 78, 242. 1762.
Moss campion, silène acaule
Cucubalus acaulis Linnaeus Sp. Pl. 1: 415. 1753; Silene acaulis subsp. arctica Á. Löve & D. Löve; S. acaulis var. exscapa (Allioni) de Candolle; S. acaulis subsp. subacaulescens (F. M. Williams) Hultén; S. exscapa Allioni; Xamilensis acaulis (Linnaeus) Tzvelev
Plants perennial, mat- or cushion-forming, subglabrous; taproot stout; caudex much-branched, becoming woody. Flowering stems erect, leafy proximally, 3-6(-15) cm, old leaves persistent at base. Leaves mostly basal, densely crowded and imbricate, sessile; blade 1(-3)-veined, linear-subulate to lanceolate, 0.4-1(-1.5) cm × 0.8-1.5(-2) mm, margins cartilaginous, often ciliolate especially proximally, apex acute, glabrous to scabrous. Inflorescences solitary flowers. Pedicels 2-40 mm. Flowers bisexual or unisexual, all plants having both staminate and pistillate flowers, others having only pistillate flowers, subsessile or borne singly on peduncle; calyx 10-veined, lateral veins absent, tubular to campanulate, (5-)7-10 mm, herbaceous, margins often purple tinged, dentate, sometimes ciliate, ± scarious, glabrous, lobes lanceolate to ovate, 1-2 mm; petals bright pink, rarely white, limb unlobed to shallowly 2-fid, 2.5-3.5 mm, base tapered into claw, auricles and appendages poorly developed; stamens exserted in staminate flowers, not so or aborted in pistillate flowers; styles 3. Capsules 3-locular, cylindric, equaling or to 2 times calyx, opening by 6 recurved teeth; carpophore ca. 1 mm. Seeds light brown, reniform, 0.8-1(-1.2) mm broad, dull, shallowly rugose. 2n = 24.
Flowering early summer. Arctic and alpine tundra, gravelly, often wet places, rocky ledges; 0-4200 m; Greenland; Alta., B.C., Nfld. and Labr., N.W.T., N.S., Nunavut, Ont., Que., Sask., Yukon; Alaska, Ariz., Colo., Idaho, Maine, Mont., Nev., N.H., N.Mex., N.Y., Oreg., Utah, Wash., Wyo.; Europe; Asia (Russian Far East).
Silene acaulis is a variable species, and most workers have recognized infraspecific taxa in North America: subsp. acaulis (subsp. exscapa and subsp. arctica), which is predominantly arctic; and subsp. subacaulescens, which extends down the Rocky Mountains from Alaska to Arizona and New Mexico. In subsp. acaulis, the leaves are flat and short and the flowers are subsessile and smaller in size. Subspecies subacaulescens is typically a larger, less-compact plant with longer, narrower leaves and larger, pedunculate flowers. However, in many populations, these two variants are poorly differentiated, and in others both occur together, connected by intermediates.
Silene acaulis is widely distributed in arctic and alpine Europe.