Nearly 400 different species of ranunculus plants (Ranunculus spp.) exist worldwide; they commonly receive names like crowfoot or buttercup. Some grow as seasonal annuals, biennials or perpetually returning perennials in woodlands, alpine screes, grasslands or bogs, and at water's edge. Generally speaking, it's best to grow ranunculus in moist, fertile soil with at least four hours of direct sun, although this requirement varies among species.
Buttercup species grow with any of four root system types. Some grow from rhizomes, underground horizontal stems with a swollen appearance--such as the giant buttercup (Ranunculus lyallii). Others develop a tuber-based root system with swollen nodules that store water and food starches, such as the lesser celandine (Ranunculus ficaria). Tuber-types are sold and discussed by horticulturists as "bulbs." Thirdly, some roots grow as "runners" or stolons, which are spreading surface stems that root where they touch the soil. Creeping buttercup (Ranunculus repens) is an example. The last type of root system is fibrous. Plants like the Persian buttercup (Ranunculus asiaticus) or bulbous buttercup (Ranunculus bulbosus) develop a matrix of thin, thread-like roots emanating from a tuber or corm, or simply from the base of the stem.
Leaves typically become a deep emerald green, although species with red-green leaves exist. As variable as the number of species, the leaves range from being entire singular blades to double-branched leaflets or multi-lobed, hand-like leaves. Many grow their leaves up directly from the roots to create a basal rosette, while others sprout upright stems with leaves clasping their bases around the stems. Such species arrange these leaves in an alternating arrangement on the stem. The sap exuded from foliage and stem causes skin irritation in some people.
In its basic form, the flower of a ranunculus bears five petals and occurs in most species in either spring or summer. The individual blossom attains a bowl-, saucer- or cup-shape and typically is yellow. Red, orange, white and pink petals are possible, too. The flower bears a rounded core of female ovaries surrounded by many male, pollen-carrying stamens that often are yellow. Flowers occur singly on stem tips or in loose, branching clusters. Some species' flowers display multiple rows of petals, a double form, that makes them look like pompoms or pleated ball masses.