1. Myosoton aquaticum (L.) Moench (giant chickweed)

Stellaria aquatica (L.) Scop.

Map 1471, Pl. 343 c, d

Plants perennial, with slender rhizomes, the stems also frequently rooting at the lower nodes. Stems 10–100 cm long, sprawling or ascending from a spreading base, unbranched or more commonly branched, moderately to densely pubescent with minute, stalked glands, often glabrous or nearly so toward the base. Leaves opposite, fused basally into a sheath, long-petiolate (basal leaves) or sessile (stem leaves), the uppermost leaves somewhat clasping, lacking axillary clusters of leaves. Stipules absent. Leaf blades 2.0–3.5(–8.5) cm long, ovate to broadly elliptic, not fleshy, angled to rounded or shallowly cordate at the base, angled or tapered to a sharply pointed tip, glabrous or the undersurface glandular-hairy along the midvein. Flowers in axillary and/or terminal clusters, 1–2(–3) cm long, erect or ascending at flowering, downward-angled from the base in fruit, the bracts paired and resembling small leaves. Epicalyx absent. Sepals 5, 4–6 mm long (becoming elongated to 9 mm at fruiting), distinct, ovate, angled or tapered to a bluntly or more commonly sharply pointed tip, not appearing hooded or awned, the margins herbaceous and green or thin and white, glandular-pubescent. Petals 5 (but usually appearing as 10), 4–7 mm long, more or less obovate, angled or tapered but not to a stalklike base, the tips deeply 2-lobed (nearly to the base), white (rarely pink elsewhere), lacking appendages. Stamens (5–)10, the filaments distinct, attached along the margin of a small nectar disc. Staminodes absent or rarely 1–5 and linear. Pistil with 1 locule, sessile. Styles 5(6), each with stigmatic area along the inner surface. Fruits capsules, 5–10 mm long, opening by 5 (rarely 6) somewhat recurved valves or teeth, these narrowly notched at the tip. Seeds 50–100, 0.8–1.0 mm wide, kidney-shaped, the surface with papillae, dark brown, lacking wings or appendages. 2n=28. May–September.

Introduced, known thus far from a single collection from Clay County (native of Europe and Asia; introduced sporadically in the northeastern U.S. west to Minnesota and Kansas). Bottomland forests.

The only collection from the state thus far was made in 1985 along the Missouri River by Jay Raveill and was reported by Rabeler and Thieret (1988).