There are primitive citrus fruit trees in the genus Serverinia. Reaching even further back in the Orange subfamily (Aurantioideae), we find the genera Afraegle and Murraya, which are hard-shelled, remote citroid fruit trees.
The various species of the genus Citrus are believed to be native to the subtropical and tropical regions stretching from eastern Asia southwards to Australia.
Botanists have calculated that the history of the citrus tree goes back twenty million years to a time when Australia was joined to Asia. This span of time is remarkable when you consider the ease with which hybridization takes place.
Although they have been cultivated for over 4,000 years in China and Southeast Asia, the grapefruit was developed only in the 18th century.
References to sweet oranges and mandarins are found throughout ancient Chinese literature. The earliest reference was from a tribute to an emperor who reigned from 2297-2205 BCE. Another from 1178 CE provides a detailed description of twenty-seven different citrus varieties.
Citrus fruits are the third most important group of fruits, with only the apple and pear, and the banana and plantain surpassing them in quantity produced and consumed. In addition, no other fruit has been as well documented or examined as the citrus.
The citrus belt is a region that follows the equator and extends approximately 35 degrees latitude to the north and south. Many commercial citrus products are restricted to the subtropics located, between 20 and 40 degrees north and south of the equator.
Productivity is greatest in areas with seasonal changes. In areas closest to the equator, where warm temperatures prevail throughout the year, citrus is grown largely for local consumption. The warm temperatures of the tropics speed growth and mature the fruit more quickly, resulting in a very short harvest period.
Climate strongly affects the growth of citrus and can affect all aspects of its growth, right down to the colour and shape of the fruit. The various shapes can be pyriform, collared, ovoid, ellipsoid, obovoid, oblique, globose or spheroid, oblate, or necked.
Heat does not necessarily produce the most vivid colours either. In fact, in tropical areas, citrus fruit often remains green when ripe. Colour tends to develop in the more arid climates where low temperatures prevail for several weeks before harvest.
Citrus from the tropics accounts for only about 10% of the world’s production. The largest producers are Brazil and the US, which grow 42% of the world’s supply; but most of that goes into processing rather than fresh consumption.
Other leading citrus producers include such Mediterranean countries as Spain, Italy, and Egypt, as well as Mexico and China.
Commercial citrus fruits have been harvested in Malaysia for less than two decades. Until then, pineapple, banana, and coconut had been the preferential revenue-generating fruits. Since Malaysia’s independence, citrus cultivation has been encouraged by government incentives. However, with the ever-increasing destruction of the Asian forests, the wild relatives of the orange, tangerine, grapefruit, lemon, and lime are now endangered.
The genus Citrus is of the family Rutaceae and comprises the many species and hybrids of orange, lemons, limes, grapefruit, citrons, tangerines, ugli fruit, ortanique (a hybrid orange), citrange (a cross between an orange and a citron); but the most widely known citrus fruits are the lemon, orange, and grapefruit.
However, citrus-types are separated into different botanical species. For example, kumquats are included with the citrus, but are of the genus Fortunella. The hybrid process has also increased the complexity of the family.
The range of citrus is enormous, taking in hundreds of varieties and subspecies to make it the most commonly propagated fruits cultivated in over 100 countries. Because the yield of the average citrus tree far exceeds that of any deciduous tree (apple, pear, peach, plum), citrus is an economic mainstay for many countries.
Several other genera within the Rutaceae family produce fruits classified as citrus, including the trifoliate orange (Poncirus trifoliata) which is a fairly cold-hardy deciduous relative that has inedible fruit. Both the bitter kumquat and trifoliate orange are mainly used as ornamentals.
One feature that gives citrus fruits, known botanically as hesperidium, a special quality is their unique structure. The outer layer or rind, known as flavedo (exocarp or epicarp), is covered with tiny pockets containing aromatic oils, and can be bitter tasting. It is used mainly as flavouring.
These pungent oils are also present in the leaves and other vegetative parts of the plant and are responsible for the distinctive aroma released when the peel is crushed or grated and are widely used in cooking and perfumery.
For example, the Bergamot orange (Citrus bergamia) is grown almost exclusively for the oil that it yields, and is in much demand by perfumers. The rind is also used in pharmaceuticals and has more Vitamin C than any other part of the fruit. The albedo, which is the inner pith (mesocarp), contains a good deal of ascorbic acid and pectin, which is used to solidify jams, pharmaceuticals, and shampoos. The pulp (endocarp) is the part of the fruit that is eaten most often.
Each segment of the pulp is a single carpel of the whole fruit. In the navel oranges, the tertiary fruit are additional carpels growing over the mature fruit. The juice is contained in the vesicles that grow from the hairlike tubes on the segment membranes and filled with cells of sap.
These vesicles contain solutions of sugars (glucose, fructose, sucrose) and acids, as well as Vitamin C and the B complex, carbohydrates, minerals, and other nutrients.
Citrus arrived in the Americas with Columbus’ second voyage, and the first plantings occurred in the “US” between 1513 and 1565 near the Florida settlement of St. Augustine along the St. John’s River.
By 1707, the citrus had spread to missions of lower California, Sonora Mexico, and Arizona. In 1822, Florida became a territory of the US, and a citrus industry quickly developed.
The St. Augustine groves were soon producing nearly three million oranges a year. Two notable groves are the Mays Grove at Orange Mills, on the St. John’s River, and the Dummitt Grove, on Merritt Island, which made the Indian River famous for its production of premium quality fruit.
Florida’s Indian River area actually encompasses a tidal lagoon, two miles wide and 120 miles long, stretching from the Florida mainland and the Atlantic barrier beaches. The official Indian River area was established in 1941 and begins ten miles north of Daytona Beach and continues south through Titusville, Cocoa, Melbourne, Vero Beach, Fort Pierce, and Hobe Sound to Palm Beach.
In California, citrus was not planted until 1834. Tulare County was seeded with citrus trees and became the most important citrus growing belt in the state. Small citrus orchards began to spring up and thrive, establishing California’s citrus economy. In 1873, Eliza Tibbets planted the most famous orange – the Washington Navel – at her home in Riverside, California, and started an agricultural phenomenon.
Gold diggers in Northern California sought out oranges from Los Angeles and San Diego until planting began in the San Francisco and Sacramento areas.
The first citrus of Northern California was planted by Judge Joseph Lewis in 1856, and still survives as the “Mother Orange”. It is the oldest and largest living orange tree in California. By 1875, transcontinental railroads brought citrus to the eastern markets, where actual sales began in 1877. By 1892, California began shipping citrus to Europe.
The essential oils are extracted by pressing on the outer part of the fresh peel. One well-known extract is bergamot oil, used in cologne and Earl Grey tea.
Bergamot has also been used for many years in Italy to treat fevers and in China to treat coughs and colds.
In France, mandarin oil is used to treat indigestion and hiccups in children. Modern science is just beginning to catch up to the reason behind these successful “folk remedies”.
Another method used is steam distillation of freshly picked flowers, which produces the orange blossom water. Essential oils have been used for centuries as folk remedies and are now used as fragrances in soaps, detergents, cosmetics, perfumes, and pharmaceuticals.
Other uses for the oils include aromatherapy, skin care, and as an aid to circulation and digestion.
In 1944, scientists found a way to concentrate the juice in a vacuum and freeze it without destroying the flavour or vitamin content. This revolutionized the citrus industy, and today, about 70% of the US orange crop goes to such processing.
Citrus also plays a major role as a raw material for other products. The fresh fruit is processed into juice, concentrates, canned, or refrigerated segments.
Other products include marmalades, cattle feed made from the skins, essential oils, pectin, and other chemicals. Oranges account for about 65% of all citrus production, 15% goes to mandarins, 10% to lemons and limes, and 10% to grapefruit.
Propagation of citrus trees involves grafting the desired variety onto a specific type of rootstock. Growers prefer budded trees over seedlings as they are reliably true to type, produce fruit sooner, have a greater tolerance to cold, have a resistance to disease, have a higher quality of fruit, mature earlier, can be dwarfed, and adapt better to soil conditions.
Citrus fruits usually bear fruit four to six years after the initial planting. Some trees are known to last more than a century. Harvesting is generally done by hand, although a mechanical process is being tried out in Florida to harvest fruits meant for juice.
Citrus groves are highly susceptible to insects and fungus; and in order to prevent an economic loss, growers resort to pesticides, insecticides, and fungicides.
More growers are finding that using natural predators to control pests is becoming the more accepted method as the “organic” food industry gains popularity. Since most conventional citrus fruits are sprayed with many different chemicals and wax, it is wise to buy organic.
Vigorous scrubbing may reduce the amount of such chemicals on the skin, but does not reach internally. It is wise never to allow children to bite into an orange, even if only to peel it.
ZEST is an important culinary feature of lemons or limes. It refers to the top colourful layer of the rind on a citrus fruit.
Zest has a more intense flavour than the juice because of its heavy concentration of oil found in the skin. It is important to remove only the top coloured layer and not the bitter white pithy layer underneath. This can be done with a knife or a grater.
Zest can be frozen or dried for later use. There is no need to defrost it or rehydrate it before using. Zest can be used as flavouring agents in thousands of savoury and sweet preparations.
Caution must be observed when zesting too many citrus fruits at once and then going outside in the sun. The peel contains psoralens, which make the skin and hair photosensitive and more prone to sunburn.
Fruit is defined as a food having a pulpy tissue that is associated with seeds. In botany, it is the ovary of a plant. According to this definition, eggplant, cucumbers, and pumpkins are all fruits.
However, the USDA prefers to define fruit as any plant food eaten as a dessert, a snack between meals, or accompanying breakfast as opposed to being the main course of any meal.
Because of domestication, many fruit-bearing plants have been altered so extensively that they cannot propogate without human intervention.
Fruits are often grouped as follows:
- Aggregates: consist of many tiny seed-bearing fruits that combine into one mass but developed from many ovaries. Example: strawberries, blackberries, and raspberries.
- Berries: are fruits from a single ovary but may contain more than one seed. Example grapes and persimmons. According to this definition, bananas are berries that have lost the ability to form seeds.
- False berries: are seedless fruits that result from a fusion of an ovary and a receptacle. Example: blueberries and cranberries.
- Drupes: are fruits that contain a single seed and develop from a single ovary. Example: cherries and peaches as well as almonds and walnuts
- Hesperidium: usually refers to the multiseeded citrus-type fruits which are enclosed by a tough skin. Example: lemons and oranges.
- Multiple fruits: are those whose ovaries and receptacles are derived from a common base to become one fruit. Example: pineapple and figs.
- Pomes: are many-seeded fruits that result from a fusion of an ovary and a receptacle. Example: apples and pears.