C. pumilum f. medium Möschl

Map 1457, Pl. 341 d, e

Plants annual. Stems 4–12(–20) cm long, erect, unbranched or branched toward the tip, densely pubescent with short glandular and nonglandular hairs. Leaves sessile, lacking axillary clusters of leaves. Leaf blades 0.3–2.0 cm long, spatulate (especially toward the stem base) or oblong to ovate, angled to a bluntly or sharply pointed tip. Flowers in open panicles, the stalks 0.3–0.6(–1.0) cm long, 1.0–1.5 times as long as the sepals, erect or ascending at flowering and fruiting, densely pubescent with short glandular hairs, the bracts green or the upper bracts sometimes with narrow, thin, white to translucent margins. Sepals 5, 3–5 mm long, lanceolate, angled to a sharply pointed tip, green or sometimes reddish-tinged toward the tip, densely pubescent with short glandular hairs, these not extending past the sepal tips. Petals 5, 3–5 mm long, about as long as or slightly longer than the sepals, notched or shallowly lobed at the tip, the veins branched. Stamens mostly 5. Styles 5. Fruits 4.0–7.5(–8.0) mm long, 1.0–1.5(–2.0) times as long as the sepals, straight or slightly curved. Seeds 0.6–0.7 mm wide, the surface with bluntly to sharply pointed tubercles, brown. 2n=72, 90–95, about 100 (most commonly 2n=72). April–May.

Introduced, scattered in the southern half of the state, most abundantly in the Unglaciated Plains Division (native of Europe, Asia; introduced in the eastern U.S. west to Michigan, Nebraska, and Texas, also in Oregon and Washington; Canada). Glades, margins of sinkhole ponds, and tops of bluffs; also pastures, crop fields, fallow fields, lawns, railroads, roadsides, and open, disturbed areas.

Cerastium pumilum is abundant in some urban areas and is probably far more common than the relatively few collections suggest. Resemblance to the larger, more common C. fontanum, as well as to the early flowering of all of the introduced annual Cerastium species, has no doubt contributed to it being undercollected. Plants of C. pumilum can be most easily confused with C. semidecandrum (all bracts with very broad, thin margins), C. fontanum (stamens 10 and all bracts with thin margins), C. glomeratum (sepal hairs longer than the sepal tips and entirely herbaceous bracts), and C. diffusum (often with 4-parted flowers and only rarely with very slender, thin margins in the uppermost bracts).