Citrus fruits: Where did they come from and how would we live without them?

The citrus family boasts an incredible diversity of fruits, each with its unique flavors, fascinating aromas, and valuable health benefits. Among this diversity, lemons and oranges take the spotlight.

But have you ever wondered where citrus fruits came from? Researchers may have found the answer.

The citrus family

We know of several speculated origins of the citrus family. This widely cultivated group of fruits has been rumored to come from the balmy jungles of northeastern Australia. Researchers have also suggested the Himalayan foothills as its origin.

However, a new study provides some clarity about the origin of citrus fruits. In this study, researchers extensively examined the genomes of the numerous species within the orange subfamily – Aurantioideae. 

Their findings point to the possibility of citrus-related fruits originating from the ancient Indian subcontinent, followed by the diversification of their flavors in south-central China.

The citrus genus

Aurantioideae is the orange subfamily. It contains more than 30 genera of fruit-bearing plants. They are widely dispersed across Asia, Africa, and Polynesia. The Citrus genus is one of the most prominent in the subfamily.

Members of the Citrus genus include oranges, grapefruits, lemons, and limes, all of which have left lasting flavors on the palates of people around the world.

Experimental design

The research team from the Huazhong Agricultural University in China was led by horticulturist Qiang Xu. The goal was to provide clearer and actionable insights into the origin and evolution of the orange subfamily. 

To achieve this, they compiled the genome sequences of 12 distinct species and cross-referenced them with 314 existing accessions from the Aurantioideae subfamily. This helped them to construct a graph-based pangenome for the group.

The team constructed a phylogenetic tree (or evolutionary family tree) from the genetic database obtained, showing the various evolutionary patterns between the members of the group. From there, they drew insights into the time and place of origin of these species.

What was learned about citrus fruits

Findings from the study point to a remarkable history that has unfolded over time. It appears that the precursors to citrus plants first existed on the Indian subcontinent about 25 million years ago.

The collision of this subcontinent with continental Asia created the Himalayas. As a result of the collision, the ancestral citrus plants also dispersed into Asia, as indicated by the citrus-like plant fossils found in southern China.

The scientists suggest that south-central China was the origin of mandarins, trifoliate oranges, and other true citrus species. They estimate that the time of origin was eight million years ago. The experts also propose that other early citrus species, including citron and pomelo, originated years later in the Himalayan foothills.

Why south-central China?

The researchers believe south-central China’s climate played a pivotal role in this evolutionary tale. The shift in climate from dry tropical conditions to a wetter climate provided the ideal growth conditions for oranges and lemons. The subsequent cultivation of citrus fruits by locals, for varying purposes, helped to rapidly grow the group’s diversity.

PH4 genes and citric acid

Expanding the scope of their study, the researchers also found major differences in how the citrus plants and their kin expressed the PH4 genes.

“The PH4 gene is important for the citric acid accumulation of fruits for both citrus and citrus relatives,” explained Xu. While non-citrus fruits had low levels of citric acid, their citrus counterparts contained high amounts. This indicates a better PH4 gene expression in the latter.

Conserving citrus fruits

Understanding the past of oranges and lemons and all citrus fruits holds promise for their future conservation. This knowledge could prove crucial for protecting wild species’ habitats. It could also aid in the preservation of genetic diversity by identifying the endangered species among the group.

More about citrus fruits

With their vibrant colors and zesty flavors, citrus fruits are more than just a delightful addition to our diet. From lemons to oranges and grapefruits to limes, these fruits bring a plethora of health benefits and diverse uses to the table. Let’s move beyond their origin story and touch upon the benefits of citrus.

Citrus elevates health

Packed with Vitamin C: Citrus fruits, notably oranges, supply a significant dose of Vitamin C, a potent antioxidant. Vitamin C boosts the immune system, aids in the absorption of iron from plant-based foods, and promotes healthy skin.

Rich in Fiber: Consuming citrus helps support digestive health. The soluble fiber present in these fruits aids in lowering cholesterol levels and helps maintain steady blood sugar levels.

Promotes Heart Health: Regularly eating citrus fruits can reduce the risk of certain heart-related conditions. The combination of fiber, potassium, and natural compounds supports healthy blood pressure and cholesterol levels.

Multitude of culinary uses

Juices and Drinks: Many people start their day with a refreshing glass of orange or grapefruit juice. Citrus juices serve as a base for countless beverages, from smoothies to cocktails.

Zests and Flavors: Lemon and orange zests add a burst of flavor to baked goods, sauces, and salads. Their essential oils elevate many dishes with a tangy twist.

Natural Preservatives: Citrus juice, especially lemon, acts as a natural preservative. It prevents the browning of fruits like apples and avocados and keeps homemade jams and jellies fresh.

Citrus fruits in daily life

Natural Cleaners: The high acidity of citrus fruits, combined with their antiseptic properties, makes them effective natural cleaners. Lemon juice, for instance, cuts through grease, brightens whites in laundry, and leaves a refreshing scent.

Beauty Enhancer: Citrus fruits play a role in skincare and beauty routines. Lemon juice acts as a natural bleach for hair and skin, while orange peel exfoliates and refreshes tired skin.

Air Fresheners: The pleasant aroma of citrus fruits purifies the air. Simply boiling citrus peels or using their essential oils can replace commercial air fresheners, creating a natural and invigorating ambiance.

Word of caution

While citrus fruits offer many benefits, consuming them in excessive amounts can lead to tooth enamel erosion because of their acidity. It’s also essential to remember that some people may have citrus allergies or sensitivities.

Citrus fruits, in all their tangy glory, serve more purposes than one might imagine. Whether boosting our health, enhancing our meals, or adding zest to our daily routines, the versatility and benefits of citrus are truly unparalleled. Embracing these fruits in various aspects of life can lead to a refreshing and healthful experience.

The study has been published in the journal Nature Genetics.

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