Cherries are related to other one-seeded stone fruits, called drupes, most closely to plums but also to peaches and nectarines. Two primary types exist: sweet and tart. Sweet cherry varieties include the deep red Bing and Lambert varieties. Cherries are harvested when ripe and do not ripen significantly off the tree. When buying sweet cherries, make sure they are large, plump, smooth and dark colored for their variety and have firm stems. The darker the cherry - the sweeter its flavor. Avoid any that are pale colored (there are a few exceptions to this based on variety) and rock hard, which indicates immature fruit, or those that are wet, sticky, bruised, excessively soft or have shriveled stems - all are signs of age. Cherries with the stems attached are desirable for once the stem is removed the cherries spoil more rapidly.