This section is from the book "Handbook Of Hardy Trees, Shrubs, And Herbaceous Plants", by W. Botting Hemsley. Also available from Amazon: Handbook of hardy trees, shrubs, and herbaceous plants.
Marsh or semi-aquatic herbs with fleshy creeping rootstocks. Leaves petiolate, cordate, glabrous. Flowers few, terminal, yellow. Sepals 5 or more, petaloid. Petals none. Carpels several, many-seeded. Name from kaxaoos, a cup.
1. C. palustris. Marsh Marigold. - A showy native plant growing on the margins of streams and in swampy places, producing its large yellow flowers in Spring. There is a double-flowered variety (fig. 9) in cultivation.
Fig. 9. Caltha palustris flore pleno. (1/4 nat. size.)