4. Cerastium L. (mouse-ear chickweed)

Plants annual or perennial. Stems erect or ascending, often from spreading, somewhat matted, sprawling bases, often branched toward the tip, less commonly unbranched below the inflorescence, sparsely to densely pubescent with sometimes woolly hairs, some of the hairs sometimes gland-tipped. Leaves opposite, fused basally into a sheath, short-petiolate (basal leaves) or sessile and sometimes slightly clasping (stem leaves), in a few species with axillary clusters of leaves. Stipules absent. Leaf blades linear-lanceolate to oblong-spatulate or elliptic to broadly ovate, not fleshy, tapered at the base, angled to a bluntly or sharply pointed tip. Flowers in terminal open or relatively dense clusters or panicles, with stalks 0.1–2.5(–4.0) cm long, erect or ascending to somewhat spreading at flowering, sometimes appearing hooked or downward-angled at fruiting, the bracts paired and resembling small leaves, often with thin, whitened margins. Epicalyx absent. Sepals (4)5, usually fused at the base, the lobes narrowly elliptic to lanceolate or broadly lanceolate, green or sometimes reddish-tinged toward the tip, tapered or angled to a bluntly or more commonly sharply pointed tip, not appearing hooded or awned, the margins thin and white or translucent. Petals (4)5 or rarely absent, oblanceolate to spatulate, tapered to a stalklike base, shallowly notched or more commonly deeply 2-lobed (to about the petal midpoint) at the tip, white or rarely tinged with purple, lacking appendages. Stamens (4)5 or more commonly 10, the filaments distinct. Staminodes usually absent. Pistil with 1 locule, sessile. Styles (4)5 (rarely 3 elsewhere), distinct, each with a stigmatic area along the inner surface or subterminal. Fruits capsules, often curved, dehiscing apically by (8)10 (occasionally 6 elsewhere) erect to spreading, often somewhat inrolled teeth. Seeds 15–30 or more, wedge-shaped to kidney-shaped, the surface tuberculate or with minute papillae, orangish brown to brown, lacking wings or appendages. About 180 species, nearly worldwide, but most diverse in Europe and Asia, introduced nearly worldwide.

In addition to the ten species treated below, C. dubium (Bastard) Guépin (anomalous mouse-ear chickweed) should be expected in Missouri. First collected from eastern North America in central Illinois in 1980 (Shildneck and Jones, 1986), it is now known from at least one population in all states adjacent to Missouri except Iowa; those in Arkansas (Crittenden and Mississippi Counties; Rabeler, 1993) and Kansas (Labette County) are particularly close to our borders. Although the short, sparse glandular hairs on entirely herbaceous bracts would place C. dubium closest to C. nutans or C. brachypodum in the key below, C. dubium can be distinguished readily by its slender, almost linear leaves and shallowly notched petals. It also is distinct in having 3(4) styles and a straight (rather than curved) capsule that opens by 6(8) teeth.

Steyermark (1963) noted that the annual species of Cerastium sometimes are collected when young in the spring and cooked as vegetables.