Prunus spp.
ROSACEAE, Rose Family
The genus Prunus includes mostly small trees, used around the world for producing sweet fruit: plums, cherries, peaches, apricots, and nectarines. We know that apricots were cultivated in China at least 4000 years ago, and peaches were also cultivated there at least 3000 years ago. In China, the peach was a symbol of immortality or longevity, springtime, and marriage. Wherever plants with sweet fruits are native, humans have undoubtedly gathered these over a long period of history. Most of the edible species originated in eastern Asia and Persia, and were carried westward across southern Asia into the Mediterranean region. Apricot trees were certainly grown in England during the reign of Henry VIII (1500) and appear to date there from a couple hundred years earlier. European settlers to North America cultivated these species in the original 13 colonies. The Spaniards introduced the peach to Florida in 1565, and peach groves were abundant in Georgia by the mid-1600s. Now we think of Georgia as "the peach state" (see the license plate!) and places in the Midwest for sweet cherry, although both California and South Carolina now produce more peaches. Most commercial apricots in the world are grown in the Central Valley of California, where also the almond is a valuable cash crop (Blue Diamond Almonds are canned in Sacramento). Marachino cherries, recolored, of course, come from Michigan. Prune trees were late arrivals into North America (1856) from France.
The almond helps us to understand the nature of the fruit, a drupe, in the vernacular often called a stone fruit. Endocarp becomes hard by forming much sclerenchyma, and this surrounds the locule in which a large seed is trapped. In almond, the endocarp is easily separated from the fleshy mesocarp; then the endocarp is split open to obtain the seed, the almond, which is about 40 to 50% oil (chiefly oleic acid). A peach also shows this structure when the "pit," i.e., the stone, breaks to reveal the seed within the locule. Cherry pits are too hard to break; in fact, the pit is more likely to cause a tooth to break than the reverse, due to the high lignin content of the endocarp.
When you eat your next cherry, peach (only 50 calories), or apricot, recognize that the skin is exocarp with a well-developed cuticle, and the fleshy portion is mesocarp. The wax is particularly abundant on the surface of certain plums, which have a bluish color from the surface wax, and sweet cherries are especially glossy due to their well-developed cuticle. The peach is unusual in having many hairs (fuzz) on the epidermis of the exocarp. Carotenoids create the yellow and orange pulp colors, as in peach and nectarine (P. persica) and the apricot (P. armeniaca), including the all-important beta-carotene (precursor of Vitamin A), and the dozen common white-fleshed peaches are a much lower source of Vitamin A. These drupes are typically rich in minerals as well, and dehydrated plums, i.e., prunes, are exceptional natural sources of potassium.
These stone fruits can be grown commercially only where the proper amount of cold temperature occurs during the winter. All types require some nights below freezing to permit proper flowering the next spring. The measure of coldness is called "chill hours." Nonetheless, each species can only tolerate certain low temperatures without permanent damage. For example, peaches are grown in Georgia, where only mild winters occurs, whereas sweet cherries do best in places like Michigan and Ohio or the Pacific Northwest, where cold winters are the rule. For example, cherries generally need exposure to four to eight weeks of freezing and near freezing temperatures. In Southern California, cherries are grown at high elevation around Julian in San Diego County, where below freezing conditions are right for that species. Almonds and apricots tend to grow where summers are hot and relatively dry, as you find them in Central California but also Turkey, Israel, and Persia (especially Afghanistan). All of these stone crops are vegetatively propagated by grafting, because you cannot be certain on the quality of fruit from seed-grown trees.
Many volumes could be written about the different varieties and clones of Prunus in cultivation. Take as an example the peaches and apricots. There are cling or clingstone, semi-cling, semi-freestone, and freestone peaches, based on how the pulp (mesocarp) separates from the stone (endocarp). Dozens of different peach clones are grown even within a single region, e.g., northern Florida and Georgia. Here in California at least 30,000 acres of cling peaches are in cultivation in the Central Valley and Sacramento Valley; there are about 140 trees per acre yielding nearly 600,000 tons of cling peaches. California production accounts for 99% of all cling peaches grown in the United States, and nearly all are canned in these counties as cling peaches and in fruit cocktail within 24 hours of being picked. Hand-eaten freestone peaches account for another 325,000 tons in California. The U.S. annual production of apricot is approximately 200,000 tons, and again, most tonnage is grown in California's Central Valley (Patterson CA "Apricot Capital of the World)". The domestic crop of peaches and apricots are harvested here from the Fourth of July until Labor Day, and the fruit peaches and apricots in our markets six months later are imported from Chile and New Zealand. Shipped peaches and apricots must be stored just above freezing. When shipped, peaches and related fruits often are lightly coated with a wax to retard water loss.
You should be cautious about chewing on the stems of Prunus, which contain cyanide. Release of hydrogen cyanide gas, from the plant compounds called prussic acid, is what mystery writers refer to as the smell of bitter almonds on the breath. Beware! You have been warned!