Plums are a diverse group of species. The commercially important plum trees are medium-sized, usually pruned to 5–6 m in height, but without pruning can reach 12 m tall. The tree is of medium hardiness and blossoms in different months in different parts of the world. Fruits are generally medium sized, between 2.5 to 7.5 cm in diameter, globose to oval, with a firm and juicy flesh. The fruit's peel is smooth, with a natural waxy surface that adheres to the flesh. The plum is a drupe, meaning its fleshy fruit surrounds a single hard seed. Mature plum fruit may have a dusty-white coating that gives them an opaque appearance. Dried plum fruits are called dried plums or prunes, although prunes are a distinct type of plum, and may have pre-dated the fruits now commonly known as plums.