Caltha palustris L.—Marsh marigold: cowslip
FAMILY: Ranunculaceae—the Buttercup Family (see Actaea)
PHENOLOGY: Marsh marigold usually flowers in April and May.
DISTRIBUTION: Marsh marigold, as the name implies, is often encountered in wet meadows, swamps, bogs, and shallow water. It can also occupy wet, shaded woodlands. Marsh marigolds will migrate onto low-lying areas of a lawn from an adjacent drainage ditch.
PLANT CHARACTERISTICS: Marsh marigolds have hollow stems, 2-6 dm tall, branched above; basal leaves: long-petioled, apically becoming progressively less petioled; sepals: 5-9, bright yellow and resembling petals. Each flower produces 4-12 follicles, 10-15 mm long.
POISONOUS PARTS: All parts of the mature plant are poisonous. Young plants are reported to be less toxic or not poisonous at all.
SYMPTOMS: Toxic principles can cause restlessness, depression, nervous excitation, stomach upset, salivation, weakness, and death.
POISONOUS PRINCIPLES: Toxins include the anemonin precursor proto-anemonin. The LD50 i.p. in mice for anemonin is 150 mg/kg.
CONFUSED TAXA: Caltha resembles several of the poisonous buttercups in the genus Ranunculus. Buttercup flowers contain nectariferous spots or scales at the base of each petal, and the fruit is a single-seeded achene. Caltha is devoid of nectifers, and the fruit is a several-seeded follicle. There are several varieties of Caltha palustris differentiated by stem and leaf characteristics; all are considered poisonous.
SPECIES OF ANIMALS AFFECTED: Humans, cattle, and horses have been reported poisoned by ingestion of marsh marigold. Like buttercups, marsh marigold is acrid and not palatable. Because the poisonous agent is volatile, Marsh marigold in dried hay is reported harmless.
TREATMENT: (11a)(b); (26); (5)-2mg subcutaneously; (27); (6)
OF INTEREST: Many members of the family Ranunculaceae contain similar toxins (see Ranunculus and Delphinium).