Rhubarb is a group of plants that belong to the genus Rheum in the family Polygonaceae.
They are herbaceous perennial plants growing from short, thick rhizomes. They have large leaves that are somewhat triangular shaped with long fleshy petioles. They have small flowers grouped in large compound leafy greenish-white to rose-red inflorescence.
While the leaves are toxic, the plants have medicinal uses, but most commonly the plant's stalks are cooked and used in pies and other foods for their tart flavor. A number of varieties have been domesticated for human consumption, most of which are recognized as Rheum x hybridum by the Royal Horticultural Society.
In warm climates, rhubarb will grow all year round, but in colder climates the parts of the plant above the ground disappear completely during winter, and begin to grow again from the root in early spring. It can be forced, that is, encouraged to grow early, by raising the local temperature. This is commonly done by placing an upturned bucket over the shoots as they come up. Because rhubarb is a seasonal plant, obtaining fresh rhubarb out of season is difficult in colder climates, such as in the UK.
Rhubarb can successfully be planted in containers, so long as the container is large enough to accommodate a season's growth.
The color of the rhubarb stalks can vary from the commonly associated crimson red, through speckled light pink, to simply light green. Rhubarb stalks are poetically described as crimson stalks. The color results from the presence of anthocyanins, and varies according to both rhubarb variety and production technique. The color is not related to its suitability for cooking: The green-stalked rhubarb is more robust and has a higher yield, but the red-colored stalks are much more popular with consumers.