Stone fruits (or stonefruits or stonefruit), in botany, refers to drupe, fruits in which an outer fleshy part (exocarp, or skin; and mesocarp, or flesh) surrounds a shell (the pit or stone) of hardened endocarp with a seed inside. These fruits develop from a single carpel, most often from flowers with superior ovaries. The definitive characteristic of a drupe is that the hard, lignified stone (or pit) is derived from the ovary wall of the flower.
More specifically, "stone fruit" refers to members of the genus Prunus, which includes plums, cherries, peaches, apricots and nectarines. It is traditionally placed within the rose family Rosaceae as a subfamily, the Prunoideae (or Amygdaloideae), but sometimes placed in its own family, the Prunaceae (or Amygdalaceae).
Peaches, nectarines, plums, apricots, and cherries are all members of the Prunus genus and are therefore closely related. They commonly are referred to as "stone fruits" because the seed is very large and hard. Although stone fruit crops can provide delicious fruit from June through September, most stone fruits are native to warmer climates of the world and therefore are very susceptible to injury from low winter temperatures. In addition, because they bloom early in the spring, the flowers frequently suffer damage from spring frosts. Because of this, the backyard culture of stone fruits is more difficult than that of apples or pears.
Nectarines also are more difficult because they are more susceptible to the disease organism that causes brown rot. Sweet cherries tend to crack as harvest nears if excessive rainfall occurs. Peaches, nectarines, and apricots generally will not bear fruit consistently when planted north of a line located roughly along Interstate 80 in Pennsylvania. Cherries and plums are a little hardier. Regardless of your location within the state, you should plant stone fruits only on the very best sites with excellent air and water drainage and protection from high winds.