21. Minuartia muscorum (Fassett) Rabeler, Sida. 15: 95. 1992.
Stellaria muscorum Fassett, Rhodora 39: 460. 1937; Arenaria muriculata Maguire; A. patula Michaux var. robusta (Steyermark) Maguire; Minuartia muriculata (Maguire) McNeill; M. patula (Michaux) Mattfeld var. robusta (Steyermark) McNeill
Plants annual. Taproots filiform. Stems erect, green, 10-55 cm, glabrous or weakly stipitate-glandular distally, internodes of all stems 0.5-2.5 times as long as leaves; wintering stems absent. Leaves not overlapping, connate proximally, with loose, scarious sheath 0.4-0.8 mm; blade straight to variously curved, green, flat, 1-veined, linear-lanceolate to oblanceolate, (5-)10-35(-50) × (0.6-)1.5-3.2 mm, flexuous, margins not thickened, herbaceous or thinly scarious, smooth, apex green, acute, flat, dull, glabrous; axillary leaves absent. Inflorescences 5-50+-flowered, open cymes; bracts lanceolate to subulate, herbaceous. Pedicels 0.6-5.5 cm, stipitate-glandular. Flowers: hypanthium shallowly disc-shaped; sepals prominently 3-veined, lanceolate (herbaceous portion narrowly lanceolate), 3-4 mm, to 5 mm in fruit, apex green, acute, not hooded, stipitate-glandular; petals obovate, 1.6-3 times as long as sepals, apex rounded, broadly notched. Capsules on stipe ca. 0.1 mm or shorter, ovoid to broadly so, 5.2-7 mm, longer than sepals. Seeds black, suborbiculate, radicle obscure, plump to slightly compressed, 0.6-0.8 mm, muriculate-papillate.
Flowering spring-summer. Prairies, meadows, roadsides; 200-500 m; Ala., Ark., La., Mo., Okla., Tenn., Tex.
Minuartia muscorum is closely related to M. patula, and is distinguished by the often longer and wider leaves, often longer distal stem internodes, consistently three-veined sepals, and shiny, black, muriculate-papillate seeds. B. Maguire (1951) treated this taxon as both a variety of Arenaria patula and a new species; see R. K. Rabeler (1992) for a review of the curious nomenclatural history.