A woman in her pomelo plantation.

A Thai farmer checks her pummelos, an ancestor of many popular citrus fruits. Credit: UNDP/Thierry Falise/LightRocket/Getty

Plant sciences

The sweet and sour story of citrus

DNA reveals when life first gave us lemons.

From sweet oranges to sour lemons, all citrus fruit traces its roots to the southeast foothills of the Himalaya, says an international team of scientists.

Fruits of the genus Citrus are among the most commonly grown worldwide, yet the group’s origins have been elusive. To investigate, Manuel Talon at the Valencian Institute of Agricultural Research in Spain and his colleagues analysed the genomes of 58 wild and domesticated citrus plants. They found that citrus spread rapidly from its origins in southeast Asia nearly 8 million years ago as monsoon rains weakened and a drier climate prevailed.

The analysis showed that lemons, limes, oranges and grapefruits all trace some of their roots to three fundamental ancestors: citrons, mandarins and pummelos. Pummelo ancestry, for example, conferred larger size.

The findings also confirm some of the branches of the citrus family’s evolutionary tree. Kumquats and desert limes had previously been attributed to separate genera, but the authors squeeze them into Citrus.