Rheum × hybridum
Rhubarb is a long-lived perennial grown for its tart leaf stalks. In the Northeast it is one of the first garden crops to arrive after winter, and old plantings often persist around former home sites.1
Only the stalks are food. The leaves contain enough oxalic acid to be considered unsafe to eat.1
Rhubarb is botanically a vegetable, although the kitchen usually treats the stalk like a tart fruit. Its acidity is the reason recipes so often give it a large amount of sugar or pair it with sweeter fruit.1
Its fruit-like culinary identity is relatively recent. The root circulated as a medicinal long before the stalk became popular; English cooks were making sweet rhubarb pies by the eighteenth century, and improved forcing methods plus cheaper sugar drove a wider boom in the nineteenth.2 Red stalk color is carried by anthocyanins and is best preserved with short cooking and little added liquid, which otherwise dilutes the pigment.2