3. Arenaria lanuginosa (Michaux) Rohrbach in C. F. P. von Martius et al., Fl. Bras. 14(2): 274. 1872.
Spergulastrum lanuginosum Michaux, Fl. Bor.-Amer. 1: 275. 1803
Plants ± strongly perennial, pos-sibly blooming first year, not matted. Taproots filiform to moderately thickened; rhizomes often present, slender, 2-15+ cm. Stems 1-80+, erect or ascending to procumbent or prostrate to trailing, green, 5-60 cm; internodes terete to angular, 1/ 3-8+ times as long as leaves, dull, retrorsely pubescent throughout or in lines, hairs minute. Leaves usually connate basally, with scarious sheath 0.1-0.5 mm, occasionally petiolate (proximal leaves) or sessile; petiole 2-5 mm; blade 1-veined, vein prominent abaxially, linear-lanceolate to narrowly elliptic or oblanceolate, 3-35 × 2-14 mm, herbaceous, margins thickened, scarious, shiny, ciliate proximally or throughout, apex obtuse or acute to apiculate, often minutely pustulate, ciliate on margins and adaxial midrib; axillary leaf clusters absent. Inflorescences axillary, solitary flowers or in proliferating, mostly terminal, leafy, 1-80+-flowered cymes. Pedicels erect to ascending (often arcuately so), or straight to widely divergent, often hooked distally in fruit, 2-40 mm, retrorsely pubescent. Flowers: sepals green, 1-3-veined, 2 lateral veins 4-3/ 4 times as long as midvein, often appearing prominently keeled proximally, lanceolate to ovate (herbaceous portion oblong or lanceolate to ovate), 2-5 mm, to 5.5 mm in fruit, apex acute to acuminate, not pustulate, glabrous; petals narrowly spatulate to obovate, 1.5-6 mm, 2-1 5 times as long as sepals or absent, apex obtuse to rounded, petals sometimes absent. Capsules ± loosely to tightly enclosed by calyx, ovoid, 3-6 mm, 5-1 2 times as long as sepals. Seeds 8-35, black, suborbicular, slightly compressed, 0.7-0.8 mm, shiny, smooth. 2n = 40, 44.
Varieties 4+ (2 in the flora): North America (including Mexico), Central America, South America.
Arenaria lanuginosa is morphologically diverse, both in our area and southward into northern South America, and is in serious need of comprehensive study. Other species in subg. Leiosperma (e.g., A. gypsostrata B. L. Turner) that occur in Mexico resemble A. lanuginosa; the nature of those relationships also requires study. We have taken the “conservative approach” of treating the two taxa that occur in the flora area as varieties.