The world of citrus fruits

Citrus plants are native to subtropical and tropical regions of Asia, 

Island Southeast Asia

Near Oceania

, and northeastern 

Australia

. Domestication of citrus species involved much hybridization and 

introgression

, leaving much uncertainty about when and where domestication first happened.

[2]

 A genomic, phylogenic, and biogeographical analysis by Wu 

et al.

 (2018) has shown that the center of origin of the genus 

Citrus

 is likely the southeast foothills of the 

Himalayas

, in a region stretching from eastern 

Assam

, northern 

Myanmar

, to western 

Yunnan

. It diverged from a common ancestor with 

Poncirus trifoliata

. A change in climate conditions during the 

Late Miocene

 (11.63 to 5.33 

mya

) resulted in a 

sudden speciation event

. The species resulting from this event include the 

citrons

 (

Citrus medica

) of South Asia; the 

pomelos

 (

C. maxima

) of 

Mainland Southeast Asia

; the 

mandarins

 (

C. reticulata

), 

kumquats

 (

C. japonica

), 

mangshanyegan

 (

C. mangshanensis

), and 

ichang papedas

 (

C. cavaleriei

) of southeastern 

China

; the 

kaffir limes

 (

C. hystrix

) of 

Island Southeast Asia

; and the 

biasong

 and 

samuyao

 (

C. micrantha

) of the 

Philippines

.

[2]

[3]

Map of inferred original wild ranges of the main 

Citrus

 cultivars, and selected relevant wild taxa

[3]

This was later followed by the spread of citrus species into 

Taiwan

 and 

Japan

 in the 

Early Pliocene

 (5.33 to 3.6 

mya

), resulting in the 

tachibana orange

 (

C. tachibana

); and beyond the 

Wallace Line

 into 

Papua New Guinea

 and 

Australia

 during the 

Early Pleistocene

 (2.5 million to 800,000 years ago), where further speciation events occurred resulting in the 

Australian limes

.

[2]

[3]

The earliest introductions of citrus species by human migrations was during the 

Austronesian expansion

 (c. 3000–1500 BCE), where 

Citrus hystrix

Citrus macroptera

, and 

Citrus maxima

 were among the 

canoe plants

 carried by 

Austronesian

 voyagers eastwards into 

Micronesia

 and 

Polynesia

.

[6]

The citron (

Citrus medica

) was also introduced early into the Mediterranean basin from India and Southeast Asia. It was introduced via two ancient trade routes: an overland route through 

Persia

, the 

Levant

 and the Mediterranean islands; and a maritime route through the 

Arabian Peninsula

 and 

Ptolemaic Egypt

 into 

North Africa

. Although the exact date of the original introduction is unknown due to the sparseness of archaeobotanical remains, the earliest evidence are seeds recovered from the 

Hala Sultan Tekke

 site of 

Cyprus

, dated to around 1200 BCE. Other archaeobotanical evidence include pollen from 

Carthage

 dating back to the 4th century BCE; and carbonized seeds from 

Pompeii

 dated to around the 3rd to 2nd century BCE. The earliest complete description of the citron was first attested from 

Theophrastus

, c. 310 BCE.

[4]

[5]

[7]

 The agronomists of 

classical Rome

 made many references to the cultivation of citrus fruits within the limits of their empire.

[8]

Lemons, pomelos, and sour oranges are believed to have been introduced to the Mediterranean later by Arab traders at around the 10th century CE; and sweet oranges by the 

Genoese

 and 

Portuguese

 from Asia during the 15th to 16th century. Mandarins were not introduced until the 19th century.

[4]

[5]

[7]

[8]

 This group of species has reached great importance in some of the Mediterranean countries, and in the case of orange, mandarin, and lemon trees, they found here soil and climatic conditions which allow them to achieve a high level of fruit quality, even better than in the regions from where they came.

[8]

Oranges were introduced to Florida by Spanish colonists.

[9]

[10]

In cooler parts of Europe, citrus fruit was grown in 

orangeries

 starting in the 17th century; many were as much status symbols as functional agricultural structures.

[11]

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