Citrus tamurana ("Hyuganatsu")

Japanese name: ヒュウガナツ （日向夏）
Scientific name: Citrus tamurana

[Overview]
An evergreen tree cultivated as a fruit tree.
The branches are dense and have thorns about 3–5 mm long.
The alternate leaves look simple, but are actually degenerated compound leaves, and are elliptical.
They have narrow 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 spherical to obovate, weighs about 200 g, and ripens pale yellow.
The top of the fruit rises slightly in a doughnut shape about 2 cm in diameter.
The rind is thick at about 6 mm, but easy to peel.
The flesh is soft and juicy, very sweet and fragrant.

[History]
It originated in Miyazaki; it was discovered in 1820 on the grounds of the Makata Yasutaro residence in Miyazaki, and is thought to be a mutation of Yuzu.
In 1887 (Meiji 20), Tamura Toshichika named it Hyuga-natsumikan (日向夏蜜柑).
The names New Summer Orange and Small Summer Orange are also by him.

[Uses]
It is eaten as a fruit and also processed into juice and other products.
The white inner rind has no bitterness or astringency and is fragrant, so it is eaten together with the flesh.

[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.
The fruit is easily damaged by cold while overwintering, so in regions where the minimum temperature falls to -3°C or below, it is better to harvest the fruit before winter.
Pests and diseases include citrus leafminer, scale insects, spider mites and aphids.
It is a food plant of swallowtail butterflies.

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