Citrus

Citrus fruits are special kinds of fruits that grow on trees and shrubs in a group called Citrus. Some well-known citrus fruits are oranges, lemons, grapefruits, and limes. People all around the world love these fruits because they smell nice and taste great.

The trees that grow these fruits originally came from places like South Asia, East Asia, Southeast Asia, Melanesia, and Australia. People there have been growing and using these fruits for a very long time. Over many years, citrus fruits spread to other parts of the world, like Micronesia, Polynesia, the Middle East, the Mediterranean, Europe, and the Americas.

Citrus fruits are very popular because they come in many different types and flavors. They often mix together in nature, which makes it interesting to learn about all the different kinds. Whether you like sweet oranges or sour lemons, citrus fruits are enjoyed by many people everywhere.

Evolution

Evolutionary history

Big citrus fruits today came from small, edible berries. Citrus plants began to change and split from one ancestor about 15 million years ago. This happened around the same time that Severinia (like the Chinese box orange) also split away. About 7 million years ago, the ancestors of citrus split into two groups: the main citrus group and the Poncirus group (like the trifoliate orange). Scientists studied the plants’ genes to learn this.

A study from 2018 in Nature found that citrus plants first grew in the foothills of the Himalayas, in areas like Assam (India), western Yunnan (China), and northern Myanmar. The three main ancestors of today’s citrus fruits are the mandarin orange, pomelo, and citron. Most common citrus fruits we eat today, like sweet oranges, lemons, grapefruit, and limes, are mixtures of these three species.

Citrus plants originally grew in warm parts of Asia, Island Southeast Asia, Near Oceania, and parts of Australia. As they spread and mixed together over time, many different types of citrus fruits developed.

Fossil record

Scientists have found very old leaves that look like citrus leaves from places like Italy and Yunnan in China. These leaves are millions of years old and help us learn about how citrus plants used to look long ago.

Taxonomy

Many citrus fruits we grow today are natural mixes or created mixes of just a few main ancestor plants, like the citron, pomelo, and mandarin. These mixes have made it tricky to sort out exactly how to group citrus plants.

Kumquats and Clymenia are now considered part of the citrus group. Some plants called false oranges, Oxanthera from New Caledonia, are also now included in the citrus group. Some scientists still separate the trifoliate orange (Poncirus) from citrus, while others include it in the bigger citrus group.

History

Citrus fruits have been moved and grown by people for thousands of years. Early sailors carried citrus trees on their journeys to new places like Micronesia and Polynesia.

Citron, a type of citrus, reached the Mediterranean area from India and Southeast Asia through old trade routes. Evidence of citron has been found in places like Cyprus, dating back to around 1200 BCE. Later, Arab traders brought lemons, pomelos, and sour oranges to the Mediterranean. Sweet oranges arrived in Europe during the 15th to 16th century, brought by people from Genoa and Portugal. Mandarins came much later, in the 19th century. Spanish colonists introduced oranges to Florida, and in cooler parts of Europe, people grew citrus in special buildings called orangeries.

Etymology

The name "Citrus" comes from old Latin. In Latin, this word meant either the citron fruit or a kind of conifer tree. The Latin name is connected to an ancient Greek word for the cedar of Lebanon, maybe because people thought citrus leaves and fruit smelled like cedar.

Description

Citrus plants are big bushes or small to medium-sized trees. They grow between 5 to 15 meters tall. They have sharp, pointy shoots and leaves that stay green all year. Their flowers are small and usually white. They often smell nice because of special oils in the flowers.

The fruit from citrus plants is called a hesperidium. These fruits can be round or oval. They are from about 4 to 30 centimeters long. They have a thick skin called the rind or peel. Inside the fruit, there are sections filled with juicy pulp. Many citrus fruits we enjoy, like oranges, lemons, and grapefruits, come from these plants. They taste sharp because of citric acid and also contain vitamin C. Citrus fruits come in many colors, shapes, and flavors.

Cultivation

Most citrus fruits grow on trees made by joining parts of different trees. These trees need sunny, warm places with good soil and water. They do not grow well in very cold weather.

The color of citrus fruits appears in places that have cool winters. In very warm places, the fruits stay green until they are fully grown. “Ripe” and “mature” mean different things. A mature fruit has stopped growing, while ripening is when the fruit changes and starts to decay. This change turns starches into sugars, reduces acids, softens the fruit, and changes its color. Citrus fruits do not ripen fast after they are picked, and they breathe more slowly.

Production

In 2016, the world made about 124 million tons of citrus fruits, with oranges making up about half. Citrus trade was worth about $15.2 billion in 2018, almost half of all fruit trade that year. Citrus production grew in the early 2000s because of more farming land, better transportation, and people wanting healthier foods. In 2019–20, about 47.5 million tons of oranges were made, mostly in Brazil, Mexico, the European Union, and China.

Pests and diseases

For a more comprehensive list, see List of citrus diseases.

Citrus trees can get sick from things like fungi and bacteria. For example, they can get a spot called citrus black spot, a sickness called citrus canker, and a problem called citrus greening, which is spread by tiny insects. These sicknesses can hurt citrus farming in places like Florida and California. Citrus trees can also be bothered by small creatures called nematodes.

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  Citrus black spot on a Valencia orange

[Chlorosis](/wiki/Chlorosis) caused by [Citrus tristeza virus](/wiki/Citrus_tristeza_virus)

[Citrus canker](/wiki/Citrus_canker), caused by the [gammaproteobacterium](/wiki/Gammaproteobacterium) _Xanthomonas axonopodis_

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  Asian citrus psyllid, vector of citrus greening disease

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  Citrus greening disease on mandarin orange

Life stages of the citrus [nematode](/wiki/Nematode),_[Tylenchulus semipenetrans](/wiki/Tylenchulus_semipenetrans)

Deficiency diseases

Citrus trees can sometimes show a problem called chlorosis, where their leaves turn yellow. This often happens when the soil is too alkaline, which stops the tree from getting nutrients like iron, magnesium, and zinc that it needs to make green leaves.

Effects on humans

Some citrus fruits have special chemicals that can affect our skin and health. If these chemicals touch your skin and then you go out in the sunlight, it can cause a bad reaction. This reaction can make your skin red and sore. One of these chemicals, called bergapten, is found in more amounts in bergamot essential oil.

Eating citrus fruits, like oranges and grapefruits, might help lower the chance of getting some illnesses.

Uses

Culinary

Many citrus fruits, like oranges, tangerines, grapefruits, and clementines, are eaten fresh. They are usually peeled and can be split into pieces easily. Grapefruit is often cut in half and eaten with a spoon. Lemonade is a favorite drink made by mixing lemon juice with water and sugar. Lemon juice is also used in salad dressings and added to fruit salad to keep it fresh.

Different parts of citrus fruits can add flavor to food. The colorful outer skin, called zest, is used in cooking. The whole bitter orange, including the peel and its oils, is cooked with sugar to make marmalade.

• Fried chicken garnished with lemon and onion

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  Calamansi, common in Philippine condiments

[Bitter oranges](/wiki/Bitter_orange) (_Citrus × aurantium_) are used for [marmalade](/wiki/Marmalade).

Marmalade, with orange peel

• Lemonade

As ornamental plants

By the 17th century, special rooms called orangeries were built in big houses in Europe to grow citrus fruits and show off wealth, like the Versailles Orangerie. Today, some people grow small citrus plants in pots or greenhouses where it’s too cold outside; Citrofortunella hybrids can handle colder weather well.

In art and culture

Lemons have appeared in many kinds of art, from old wall paintings to modern paintings. One famous old painting shows a person holding a lemon from long ago in Egypt. Later artists also painted pictures with lemons in them.

Citrus fruits were special treats for important people in ancient times. In a popular book from the 1800s, a character talks about how children traded limes for small toys and gifts.