Rhubarb is a perennial plant grown for its firm, tart, reddish-pink stalks; botanically it's a vegetable, but it's used in the kitchen like a fruit. Only the stalks are eaten: the leaves contain enough oxalic acid to be toxic and should be discarded. Its sharp tartness needs sweetening to balance, which is why it's most often paired with sugar and other fruit, classically strawberries, in pies, crumbles, and jams, though it also turns up in savory sauces and marinades in some cuisines. It needs a cold winter dormancy to grow well, which makes it a spring crop through most of the US, UK, and northern Europe.