Know Your Citrus

Scott Bauer, USDA
Scott Bauer, USDA / Scott Bauer, USDA

As winter approaches, you might notice that peaches and plums are disappearing from the produce aisle, and berry prices are going through the roof. But look! The new citrus fruit is here to give us a taste of the tropics in time for the winter holidays. Citrus fruits all belong to the genus Citrus, and can be hybridized with each other. The citrus fruits we know were developed from just a few that occur in the wild, including citron, pomelo, and mandarin. The variety of citrus fruits we encounter at the grocery store in the winter months are mostly hybridized from those species and their descendants.


Photograph by Johann Werfring.

Citron (Citrus medica) is the citrus fruit that gave “citrus” its name. Records of the fruit go back thousands of years in Mesopotamia, although its origin may be India or Southeast Asia. Citron is more temperature-sensitive than other commercial citrus grown in the U.S. but flourishes in South America and the coastal areas of the Mediterranean. Americans are mostly familiar with citron as a candied ingredient in fruitcake, made from the fruit’s peel.


Photograph by Forest & Kim Starr.

The pomelo (Citrus grandis) is the largest of all citrus fruits. They can grow up to nine inches in diameter and weigh over four pounds! Pomelos are native to Southeast Asia, but are gaining popularity worldwide. They appear green or yellow when ripe, and the flesh is white or shades of pink. The taste is like a sweet grapefruit, and in fact, grapefruit is sometimes called pomelo and the pomelo is sometimes called Chinese grapefruit, although they are different fruits.


Photograph by Flickr user Lotte Grønkjær.

The mandarin (Citrus reticulata), or mandarin orange, is one of the oldest citrus fruits, and the ancestor of many other fruits we know. It is a small, sweet-tasting orange originating in Southeast Asia. Mandarins are also distinct from oranges in that they are easy to peel. It has some close relatives that are sometimes hard to distinguish. Tangerines (Citrus tangerina) are closely related to mandarin oranges, although the name is usually reserved for the more reddish fruit. They are named after the city of Tangier, Morocco, from where they were exported to Europe. Clementines (Citrus ×clementina) are hybrids developed from crossing a Mandarin orange and a sweet orange. They are sweeter than tangerines, but just as easy to peel. Clementines are usually seedless, and are sometimes referred to as “seedless mandarins.”


Photograph by Morlawmina.

Oranges (Citrus sinensis) are the citrus fruit we are most familiar with. They do not exist in the wild, but were cultivated in Asia since ancient times. It is thought that the first oranges were hybrids of the pomelo and the mandarin. Oranges were brought to the Middle East in the 9th century, and into Italy by 11th-century Crusaders. By the 15th century, they had been introduced to Europe, and soon after, trees were being grown in the Caribbean Islands and in Florida. However, orange trees are temperature sensitive and the fruit was difficult to transport over long distances, so the fruit was rather expensive for most people. They were considered a real treat for the holidays, which explains their association with Christmas. Your parents or grandparents will likely remember how special it was to see an orange in the toe of their Christmas stocking.

That changed in the 1920s, when canned orange juice began to be marketed as a health drink. Vitamins were pushed as the new miracle cure, and the National Fruit Growers Exchange took advantage of the craze to promote orange juice. But orange juice didn’t really take off until frozen orange juice concentrate was developed in 1948. Frozen concentrate could be shipped all over at a fraction of the price of whole oranges, without spoiling. Plus, the growers’ orange crops could be preserved year-round. Orange juice was pushed as a natural and healthy breakfast drink, a campaign which worked wondrously. However, in the past decade, sales of orange juice are down in comparison with other juices and fresh fruit.


Image by א (Aleph).

Grapefruit (Citrus x paradisi) is a hybrid derived from pomelos and sweet oranges. It is believed to have been an accidental hybrid arising in Barbados and Jamaica in the 18th century. The name came from the tendency of the fruits to grow in clusters resembling huge grapes. The grapefruit was a novelty fruit outside of Florida until the 1930s, when the Grapefruit Diet was introduced. The diet recommended that a half a grapefruit be eaten before each meal. Those on the diet lost weight, but it wasn’t because grapefruit enzymes burned fat, as was often said. It was more likely because the low-calorie grapefruit filled the dieter’s stomach, causing them to eat less of other foods.


Photograph by Gareth Bogdanoff.

A tangelo (Citrus X tangelo) is a hybrid derived from crossing a mandarin and a grapefruit. Tangelos are juicy, brightly-colored, and have a loose peel that’s easy to remove. They also have a distinctive “neck” that protrudes from the sphere. Ugli fruit is a variety of tangelo with a not-quite spherical shape, believed to have been an accidental hybrid of grapefruit and mandarin that occurred in Jamaica around 1917.


Photograph by Flickr user Choo Yut Shing.

Kumquats (Citrus japonica) are tiny, oval-shaped citrus fruits. Sometimes the fruit is placed in the genus Fortunella instead of citrus. Kumquat trees are hardier than other citrus plants and can be grown at more northern latitudes. The fruit can be eaten whole, peel and all, except for the seeds. They are also pickled, candied, and used to flavor tea.


Photogaph by Flickr user Susy Morris.

Lemons (Citrus × limon) possibly originated in India, and are thought to be a hybrid of the citron and the bitter orange. Lemons are so acidic that they are used as flavoring and as an acidic preservative rather than a fruit. As Peter, Paul, & Mary put it: 

Lemon tree, very pretty, and the lemon flower is sweet But the fruit of the lemon is impossible to eat.


Photograph by Steve Hopson.

The name lime encompasses about a dozen species of citrus fruit that are generally green and lemon-shaped. They are almost as acidic as lemon but have their own distinct flavor. Like lemons, they are mainly used as a flavoring agent. In 1747, British Royal Navy surgeon Dr. James Lind discovered that citrus fruits could prevent scurvy, a disease which particularly afflicted sailors who spent months at sea. In 1795, the navy began carrying lemons to provide sailors with vitamin C. However, limes were easier to get in the Caribbean islands ruled by the British, so they switched to limes. It was only later found that lemons have two to four times the vitamin C of limes, depending on the variety.