Citrus fruits have always been my personal favourite fruit. If I could grow them I would, having a great big orange or grapefruit tree would be just perfect. As luck would have it I live in Canada, but I do grow small citrus fruits in pots, leaving them indoors most of the year.
What are citrus fruits? A genus of flowering trees from the Rue family, or Rutaceae. Citrus genetics are complicated and Citrus taxonomy is its own article on Wikipedia. I hope to give a brief overview on a familiar, but complex genus of plants.
Interbreeding between all citrus plants is very easy and this gives rise to many different cultivars and hybrids. For example, the navel orange is thought to be a hybrid between the mandarin orange and the pomelo. How many different wild species are there? Many, but here are some worth knowing about:
Papeda (Citrus papeda) - possibly the most basal species of citrus. Known for its rough rind, unpalatable fruit and hardiness. Cultivated species of this are mostly native to Asia, such as yuzu, kaffir lime, kabosu and sudachi.
Mandarin orange (Citrus reticulata) - the most palatable wild citrus. The fruits are smaller, sweeter, oblate and with a very thin peel that easily comes off. These traits make it very desirable in the breeding of citrus species. The centre of origin is thought to be around Vietnam, southern China and Japan. The tangerine is the main cultivated form of pure mandarin orange.
Pomelo (Citrus maxima) - the giant of the citrus world. The fruits are massive, but with a thick rind and tame tasting fruit. It's still very juicy and is sold in many grocery stores. More popular in Asia, the pomelo has been cultivated in its original form since prehistoric times. The grapefruit is the main hybrid species descended from pomelos.
Citron (Citrus medica) - A large lemon-like citrus with a thick rind. Another ancient fruit, it has mention in religious texts and is even used in special ceremonies. It is the obvious parent of lemons and related species.
So how are the species we see today all related? Well the simple answer is: It's complicated. Oranges are thought to have genetics that are approximately 25% pomelo and 75% mandarin orange. Grapefruits are another cross of the same two, but more heavily weighted towards the pomelo ancestor. Lemons are a hybrid of citron, pomelo and mandarin orange ancestry but with most of the genome coming from citrons.
There are many more citrus types still and more being bred every year. This article doesn't even mention the related species such as kumquats and Australian limes which are very interesting on their own. With kumquats, you can even eat the rind.
I hope you found this article enlightening, and if you've ever wondered where the citrus fruits at the grocery store originally came from, now you have a clearer picture. Almost all citrus varieties we consume are hybrids!
All photos taken are my own from a trip to Florida and free to re-use in your citrus and nature-related articles
