Volkamer lemon, Citrus volkameriana
© C. Jacquemond / INRA

Citrons were grown in Mesopotamia by 4000 B.C. Most other types of citrus originated in north west or south-east Asia. The first written mention of citrus fruit is found in Sanskrit literature  around 800 B.C. The cultivation of citrus fruit presumably began in China around 500 B.C. The first citrus fruit to come to Europe was the citron, which was brought by the army of Alexander the Great in 325 B.C. from Persia. The citron was first used as a perfume and an insecticide and was later found to be edible when properly prepared. The Romans imported oranges and lemons from their provinces as expensive luxuries for their banquets. The plants they grew in Rome survived but bore few fruit.

The Arab conquerors brought many novelties and inventions to Europe. Our diet was enriched by the introduction of the sour orange around 900 - 1100 A.D. The lemon arrived with returning crusaders in the first and second centuries of the second millennium. We know that lemon was grown in Sicily around 1000 A.D. and in southern Spain about 1150 A.D. The great voyages of discovery not only enlarged our view of the world but also introduced us to the sweet orange and lime in the early 1500's. The last of the common citrus fruit to arrive in Europe was the mandarin as late as the beginning of the 19th century. Since then it has become one of the most popular citrus fruits and a source of continuous development and breeding. The research centre of the French Institute for Agricultural Research on the island of Corsica in the Mediterranean has more than 240 different kinds of mandarin trees.

                                          Production areas

The largest areas of citrus cultivation are Brazil and the Mediterranean basin (where Spain is the leading country) the United States and China. Together these four areas produce three quarters of all citrus fruit in the world.  The biggest producers of orange juice are Brazil and Florida. A new feature that has emerged in the last few decennia is the year-round availability of citrus fruit in the biggest consumer areas of North America and Europe. Because of the development of new late maturing cultivars the first ripe fruit of the new season are available in South Africa, Argentina, Australia and Brazil before the previous crops are finished in the northern hemisphere. After six months the situation is reversed.

It is important to remember that unlike most other commercially grown fruit the majority of the citrus fruits (oranges, mandarins, lemons, citrons and most grapefruit) mature during the local winter. In Europe the high season is from November to March. Including the early and late varieties the whole season lasts from October to May. Citrus fruit of the tropical climate (limes, pomelos and some grapefruit types) are an exception to this. Some pomelos can bear four crops in a year and some limes are picked once a month throughout the year.

The botanical classification of citrus fruit is difficult due to several factors.  All citrus fruit hybridise easily. New hybrids are continuously developed to obtain desired qualities such as seedlessness, juiciness and fresh taste. New hybrids are spontaneously born due to cross-pollination. The differences between a new species, a new botanical variant, a different cultivated (horticultural) variety and a minor modification can be small indeed. In the case of older varieties and hybrids the most modern methods of DNA research are sometimes needed to distinguish different varieties from each other.


                    Risso, Swingle and Tanaka
Famous historical classifications include that of Risso & Poiteau from 1818. The best known recent classifications, on which this presentation is based, are those by Walter T. Swingle (US) published in 1943, and by T. Tanaka (Japan) first published in 1954. Swingle combined all citrus fruit into 16 species and their subspecies and different cultivars. Tanaka divided his citrus fruit into 159 species. This presentation is a combination of both. The main division into eight groups (limes, sour oranges, pomelos, lemons, citrons, grapefruit, mandarins and sweet oranges) follows Swingle. The division into species inside these groups mainly follows Tanaka. This is because in spite of several serious attempts the present author has not fully understood the system followed by Mr. Swingle.

Of modern botanists D.J. Mabberley (b.1948), since 2005 president of IATP, deserves a chapter of his own. He has presented the most interesting new views of citrus and the relationships between "the true citrus types." In his paper on native Australian citrus types ³  he includes the genera Microcitrus and Eremocitrus in the genus Citrus. In A classification for edible Citrus ⁴   he states that there are only three citrus species, which then are involved in several hybrids:
 
1. Citrus medica, citron, which is involved in  
2. Citrus maxima, pomelo, which is involved in   3. Citrus reticulata (mandarin). This includes mandarin, satsuma, clementine and tangerine.

According to Mabberley: "This scheme provides a workable system for botanists and fruit-growers alike."

The actual division into eight groups in this presentation however, is done by the present author
and has taken into consideration some of the most recent findings of modern research using  molecular analysis. Sometimes the division into groups is done solely by the food use of each fruit. Thus the fruits in the lime group are not all closely related. In fact it is a collection of several different kinds of citrus fruit that are used in the kitchen in a way similar to limes. The same is true of lemons. The only completely homogeneous groups are pomelos, grapefruit and sweet oranges, all of which contain cultivated varieties of only one species or hybrid. Around 175 different types of citrus fruit are presented with a brief description of the most common food uses and a photograph. Another 155 closely related cultivated varieties are mentioned bringing the number of varieties to approximately 330. The index contains around 235 alternative botanical names for the 97 citrus types that at one time or another have been deemed valid species and were thus given a botanical name.

The botanical name of each type is given first. The complete scientific name of a plant includes the name of the author, the person who first described the fruit and named it. Sometimes two authors are given: first the name in brackets of the person who originally used the Latin name followed by the name of the person who later amended the description and reassigned the name to the plant type in question. An author name is given for species and subspecies. Cultivated varieties usually do not carry author names.  An author name is often given as an abbreviation. Only Carl von Linné has an initial (L.) Where needed or available, several synonyms of the Latin name are given each with their authors. This is followed by a short description of the most common food uses. Common names follow, first in English, sometimes with local variations. These are followed by the most common names in a handful of selected languages, when available. The author is fully aware of the enormous range of geographical variants. On the Photos & links page there are links to several sites presenting large indices of names of citrus types and cultivated varieties in multiple languages.