Caltha palustris L.

Marsh Marigold, Cowslip

Caltha palustris plant2

Family - Ranunculaceae

Habit - Perennial forb with thick, fleshy roots.

Stems - Sprawling, ascending, or erect, to 60 cm, stout, furrowed, hollow, glabrous.

Caltha palustris stemStem.

Leaves - Basal and alternate, simple, unlobed, short to long petiolate. Blades 3.0-5.5 cm long, 5-10 cm wide, circular to somewhat kidney-shaped, the base deeply cordate, the tip broadly rounded, the margins finely and usually bluntly toothed.

Caltha palustris leaf1Leaves adaxial.

Pressed leaf.

Inflorescence - Solitary flowers, or open clusters of up to 7 flowers, at stem tips.

Caltha palustris inflorescenceInflorescences.

Caltha palustris inflorescence2

Flowers - Actinomorphic, perfect. Sepals 5 or sometimes more, 11-22 mm long, 5-14 mm wide, ovate to obovate, rounded at the tip, plane, yellow, not persistent at fruiting. Petals absent. Stamens numerous, prominent but scarcely showy, the anthers yellow. Staminodes absent. Pistils 3-12, each with about 15 ovules, the style rather short.

Caltha palustris flowerFlower.

Caltha palustris flowerSepals.

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.

Caltha palustris fruitsFruits.

Flowering - April.

Habitat - Wet meadows, swamps.

Origin - Native to U.S.

Lookalikes - Ranunculus ficaria.

Other info. - This pretty inhabitant of swamps was first reported from Missouri in 1987, from Lafayette County. So far, that is the only reported occurrence in the state. However, farther to our north and northeast, the plant becomes very common. It is found in nearly every county of Michigan, for example, and that is where the above images were obtained. The flowers are typical for plants in the Ranunculus (buttercup) genus, and in fact this plant somewhat resembles Ranunculus ficaria (lesser celandine), except that the flowers of that plant typically have 7-10 petals. The fruits are also multi-seeded follicles rather than the Ranunculus achenes.

The specific epithet "palustris" means "swamp loving." The bright yellow flowers of C. palustris show up well against the drab winter colors of swamps and wet places. In Illinois the plant has been used as a high-visibility indicator of swampy areas during aerial surveying. Traditional uses have included numerous medicinal applications. A root tea was used to induce sweating and as an expectorant, and a leaf tea was used as a laxative. However, the foliage is considered toxic and can poison browsing herbivores such as cattle and horses. The toxic principle is a simple compound called protoanemonin, which is found in all members of the Ranunculaceae. This compound belongs to a recognized class of toxins known as Michael acceptors. In addition to liver toxicity and other systemic effects which result from ingestion, skin exposure to the plant's juice can also cause irritation and blistering.

Photographs taken off Hwy 41, Menominee County, MI., 4-30-04 (DETenaglia); also at Yankee Springs, Barry County, MI, 5-19-2013 (SRTurner).