Mountain citron facts for kids

Citrus halimii, also known as the mountain citron, is a type of citrus fruit. Its fruit tastes sour. For a long time, scientists thought it belonged to a group called papedas. But now, they know it's a wild citrus species that is actually very close to kumquats. It is not related to the common citron. This special tree was first found and written about in 1973.

Where Does the Mountain Citron Grow?

Citrus halimii is quite rare and not many people have studied it. After it was first found and described in 1973, it has only been seen in a few places. These places are spread out across Southeast Asia. You can find it in Thailand and Malaysia, which is where it was first discovered. There are also a few isolated groups of these trees in Indonesia.

What Does the Mountain Citron Look Like?

Citrus halimii is a medium-sized evergreen tree. This means it stays green all year round. When it is fully grown, it can be about 20 to 25 feet tall. It has fewer thorns than many other citrus trees. Like other papedas, the mountain citron has fairly large leaves. Each leaf has a long, winged petiole, which is like a small stem that connects the leaf blade to the branch.

The fruits of C. halimii can be eaten, but they are sour. They are round and small, usually about 5 to 7 centimeters across. The skin of the fruit is quite thick. When it ripens, it turns yellow or orange-yellow. Inside, the thick skin is tightly attached to the fruit's flesh. The fruit has yellow-green sections. These sections are filled with many large seeds and only a small amount of juice.

How Scientists Understand the Mountain Citron

For a long time, it was hard for scientists to figure out exactly where the mountain citron fit in the citrus family. They weren't sure if it was a natural mix of two different plants (a hybrid) or a completely wild species.

Some early studies placed the mountain citron in a group of citrus called Papeda. This group was created by a scientist named Walter Tennyson Swingle. However, scientists later found that this "Papeda" group was not a true family group. It contained plants that were not closely related.

In 2022, a new study looked closely at the genes of the mountain citron. This study showed that the tree has very low levels of genetic variation. This means it is likely a true citrus species and not a hybrid. The study also looked at its genes and the special oils it produces. These clues showed that the mountain citron is most closely related to kumquats.