14. Sagina L. (pearlwort)

(Crow, 1978)

Plants annual or perennial. Stems erect or ascending to sprawling or spreading, usually branched, sometimes matted, glabrous or sparsely to moderately pubescent with stalked glands. Leaves opposite, fused basally, into an often cup-shaped, thin sheath, sessile, sometimes with axillary clusters of leaves at some nodes. Stipules absent. Leaf blades linear to narrowly triangular, somewhat stiff and leathery or sometimes softer and slightly succulent, tapered at the base, angled or short-tapered to an abrupt, minute, sharp point. Flowers in terminal or axillary open clusters or appearing solitary, the stalks erect to spreading at flowering, at fruiting sometimes hooked near the tip, the bracts of terminal inflorescences paired and resembling small leaves. Epicalyx absent. Sepals 4 or 5, distinct, ovate or elliptic to nearly circular, green or purplish-tinged, angled to a bluntly or sharply pointed tip, not appearing hooded or awned, the margins thin and translucent, white, or more commonly purplish-tinged, the surfaces usually glabrous. Petals absent or (1–)4 or 5 and inconspicuous, elliptic to oblong-obovate, angled or tapered but not to a stalklike base, the tips entire (slightly notched elsewhere), white, lacking appendages. Stamens 4, 5 (8), or 10, the filaments distinct. Staminodes absent. Pistil with 1 locule, sessile. Styles 4 or 5, distinct, each with the stigmatic area subterminal or along the inner surface. Fruits capsules, dehiscing apically to below the midpoint by 4 or 5 valves. Seeds numerous (more than 100), obliquely triangular with a distinct groove along the dorsal margin (elsewhere sometimes plump and lacking the groove), the surface smooth, pebbled, or tuberculate, light tan to brown, lacking wings or appendages. About 20 species, North America, Central America, South America, Europe, Asia, Africa; most diverse in north-temperate regions.

In addition to the two species treated here, S. japonica (Sw.) Ohwi (Japanese pearlwort) has been spreading westward since the first collections in eastern North America were made in the 1940s, and eventually it may be found in Missouri. It was collected in Ohio in 1987 (Rabeler, 1996), in Ontario, Canada, in 1995 (Rabeler, 1996), and in Illinois originally in 1951 and more recently in 1997 and 1999 (Tucker, 2000). Sagina japonica would key closest to S. decumbens, but it is distinguished by its seeds, which are plump, obovoid to globose, lack a distinct groove, and have a dark brown surface that is either tuberculate or slightly pebbled.