1. Caltha palustris L. (marsh marigold, cowslip)

C. palustris var. palustris

Pl. 512 a, b; Map 2347

Plants perennial herbs, with thick, fleshy roots. Stems 20–60 cm long, erect or ascending, relatively thick and hollow. Leaves in a basal rosette of 3–6 and several alternate stem leaves, long-petiolate (the stem leaves with shorter petioles than the basal ones). Leaf blades 3.0–5.5 cm long, 5–10 cm wide, simple and unlobed, circular to somewhat kidney-shaped, the base deeply cordate, the tip broadly rounded, the margins finely and usually bluntly toothed. Inflorescences of solitary flowers or open clusters of up to 7 flowers, at the stem tip. Flowers actinomorphic, perfect. Sepals 5(–9), 11–22 mm long, 5–14 mm wide, ovate to obovate, rounded at the tip, plane, yellow, not persistent at fruiting. Petals absent. Stamens prominent but scarcely showy, the anthers yellow. Staminodes absent. Pistils 3–12, each with about 15 ovules, the style rather short. Fruits cylindrical follicles, the main body 7–10 mm long, the fruit wall thick, prominently veined or not, the outer layer brown to dark brown, the beak 1–2 mm long, straight or curved. Seeds 10–15 per fruit. Receptacle not much enlarged at fruiting, the fruits in a ring. 2n=24–80. April.

Known thus far only from Lafayette County (northern U.S. [including Alaska] south to California, Missouri and North Carolina; Canada, Europe, Asia). Fens, in saturated soil, sometimes emergent aquatics.

Caltha palustris was first reported for Missouri by Gremaud (1988), based on his investigations of tiny, remnant fen communities entirely surrounded by crop fields in a heavily agriculturalized part of Lafayette County. These endangered habitats have yielded a number of other regionally rare plant species, including Berula erecta (Huds.) Coville (Apiaceae), Doellingeria umbellata (Mill.) Nees (Asteraceae, reported as Aster pubentior Cronquist), and Eupatorium maculatum L. (Asteraceae, reported by Ladd [1990]), that were state records.