Citrus sphaerocarpa ("Kabosu")

Japanese name: カボス （香母酢）
Scientific name: Citrus sphaerocarpa

[Overview]
An evergreen tree cultivated as a fruit tree.
The branches have sharp thorns.
The alternate leaves look simple, but are actually degenerated compound leaves, and are elliptical.
They have broad winged petioles.
The flowers are white and 5-petaled.
Many stamens are fused up to the middle of the filaments, forming a staminal tube.
The fruit is nearly spherical, weighs 100–150 g, and ripens yellow.
The top of the fruit rises slightly in a doughnut shape about 2.5 cm in diameter.

[History]
It is cultivated mainly in Oita, and old trees over 100 years old can be found in various places in the prefecture.
The place of origin is said to be Minamikaibe District in Oita, but this is not certain.

[Uses]
The strongly sour, distinctively fragrant juice is used in cooking as a vinegar.
It is also used in processed products such as juice and confectionery.

[Cultivation]
Propagate by grafting.
It prefers a sunny, well-drained location with good water retention.
Young trees transplant easily, but mature trees are difficult to transplant.
For plants in the ground, watering is unnecessary unless sunny weather continues and the soil dries out, but for young trees, watering well in summer to make the branches grow long speeds up growth.
In spring and autumn, apply organic fertilizer or a fast-acting chemical fertilizer.
If the branches become too dense and the inside of the crown gets too little sunlight, the branches die.
Dead branches cause pests and diseases and reduce fruit set, so around March prune and thin moderately so that sunlight reaches the inside.
If many fruits set, thin them in July–August.
Pests and diseases include citrus leafminer, scale insects, spider mites and aphids.
It is a food plant of swallowtail butterflies.

[Notes]
The Japanese name is thought to be a corruption of Kabusu, another name for Daidai.

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