Cherries are one of the most commonly grown home orchard fruits in the world. Practically all of the 600 cultivated fruit varieties are descended from one of two ancestors: sweet cherries (Purnus avium) and sour or tart cherries (P. cerasus). These close relatives of peaches, apricots, and plums are classified as stone fruits because the fleshy moist pulp encloses a single hard stone that bears a seed. Trees bearing sweet cherries are stately and can grow upwards to 35 feet in height. However, trees that produce tart fruits are hardier and grow more easily than the sweet varieties.