There are over 100 species of Ranunculus, with several hundred more cultivars and varieties, according to the United States Department of Agriculture's Germplasm Resources Information Network. The plants range greatly in appearance and hardiness. Some are annuals, while others are perennials. Many are simply called "buttercups." Those that grow from bulbs are the most popular with home gardeners, who find them desirable for their ease of care and colorful appearance.
The Ranunculus family is very large, and widespread throughout the United States and Europe. Some species, such as the Persian buttercup, have been cultivated for use in home gardens. Others, like the creeping buttercup, are considered a weedy plant in many states, according to the United States Department of Agriculture plant profile.
Ranunculus plants usually feature feathery, true-green foliage that is similar in appearance to the foliage of celery plants. Many of the smaller, weedy ranunculus plants have single-petaled, yellow flowers, but the bulb ranunculus species come in a wide variety of colors, from pale pastels to vibrant jewel tones, and feature papery flower petals with many layers.
Ranunculus plants range from only a few inches tall to over a foot and a half in height, depending on the species. The flowers can be less than an inch across, as in the case of the common buttercup, or half a foot wide, as in the case of the Persian buttercup. Those that grow in mounds can get up to 12 inches wide, according to the National Gardening Association.
While the specific needs of ranunculus plants can vary by species and cultivar, in general, these hardy plants can adapt to almost any type of soil as long as it is well-draining. Most, however, prefer rich, loamy soil. Overly wet soil will quickly rot the bulbs or shallow roots of the plants. Ranunculus flowers will grow in full sunlight or partial shade.
All parts of ranunculus plants are poisonous, according to North Carolina State University. If ingested in large amounts, the plant can cause vomiting, stomach and mouth pain, and intestinal upset. If the sap of the ranunculus comes into contact with the skin, it can cause redness, pain and even blisters in people who are sensitive to the plant. The irritation is usually minor and fades quickly.