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Although they appear quite attractive and benign when sporting their 1-inch diameter flowers from about mid-April to June in our area, buttercups (Ranunculus spp.) spread easily and can soon invade large areas of uncultivated land and pose a threat of toxicity to grazing animals. As a rule, horses, cattle and other livestock avoid consuming the fresh plant and this permits it to make mature seeds and remain invasive. However, if for any reason animals do ingest fresh buttercup, a toxic glycoside (ranunculin) within the flowers, leaves and stems will cause severe blistering of the mucous membranes lining the entire gastrointestinal tract, and protracted bloody diarrhea will ensue. (Humans are also susceptible to the effects of this glycoside, so one should never consume any part of the plant or permit direct skin contact with the plant juices.)

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While the juices from a fresh plant are a well-known irritant to animals, the dried buttercups that may become part of a hay crop do not have any significant toxic effects on animals because the ranunculin is partially decomposed upon desiccation. However, milk from cows that have consumed buttercup-contaminated hay may have an unpleasant off-flavor.

Many of the wildflowers that we assume to be native to our area are, in fact, species that were introduced to North America by the earliest of European explorers and have become "naturalized" in wide areas of our continent during the past 500+ years. In southern New England, where an estimated one-third of all current plant species are "non-native", common or tall buttercup (R. acris) is one of our most familiar wildflowers. Also known as meadow buttercup, or tall crowfoot, this golden-yellow flowered perennial was brought to our country for medicinal purposes by the earliest colonists from central and northern Europe. There is also a buttercup species (R. repens) that is native to North America and is known as creeping buttercup. The main differences are in growth pattern and means of propagation: common buttercup is erect, 2-3 feet tall, and reproduces by seed, whereas the creeping variety may stay as short as 6- 12 inches, with 1-2 foot long, prostrate runners that take root at each node, and can propagate by either seed or stolon.

Since antiquity, the juice from the fresh stems, leaves, and roots of both buttercups, have been used in caustic external preparations for the removal of warts and parasites (mites and ringworm) on animals and humans, as a topical analgesic for arthritis, rheumatism, and migraines, and in poultices for the treatment of boils and abscesses. But for the past century in the U.S. and Canada, as well as much of Europe and Australia, buttercups have undergone a major decline in medicinal use and now are generally regarded as noxious, toxic wildflowers of pastures, hay fields, roadsides and lawns.

Therefore, if you provide fresh pasture for one or more grazing animals, be on the lookout for either of these species of buttercup. They are blooming profusely at this time of year and are quite easily identified by their cup-shaped flowers, with 5-7 butter-colored petals. Hand- grubbing the entire plant, including the roots, before seed maturation will successfully eliminate the plants but may not be practical if the hay field or pasture area is large or heavily cursed with the weed. In those cases, thorough tillage for a season or two will be needed to eradicate the infestation. Chemical herbicides have been used with a degree of success, but pesticide resistance by buttercup has been repeatedly documented and, thus, other means of control should be employed.

Also See the Cornell University Toxic Plant Database

Prepared by Paul E. Stake, Extension Livestock Specialist, University of Connecticut Cooperative Extension System, Storrs, CT 06269-4040