Citrus depressa

Japanese name: シイクワシャー
Scientific name: Citrus depressa

[Overview]
An evergreen small tree 3–6 m tall, cultivated as a fruit tree.
Young branches are green with 2–3 ridges and often bear thick, sharp thorns 1–1.5 cm long.
The leaves are alternate, ovate-elliptic, 3–6 cm long and 2–4 cm wide, with a shallowly two-lobed tip and a margin that is entire or has very shallow teeth.
They look like simple leaves, but are reduced compound leaves.
The flowers are borne 1–3 in the leaf axils of the current year's branches, or several together in short racemes.
The flowers are white, 5-petaled and fragrant.
Many stamens are fused up to the middle of the filaments, forming a staminal tube.
The fruit is a flattened sphere 4–5 cm across and 2.5–3 cm long, ripening yellowish red.

[Uses]
The juice is too sour to eat raw, but is used as vinegar and for processing.

[Cultivation]
Propagate by grafting.
It prefers a sunny, well-drained site.
It is not very cold-hardy and requires an average annual temperature of 16°C or higher and winter lows of -3°C or higher.
Care is also needed in humid summers.
If left alone, the branches grow too dense, the inside of the crown receives too little sunlight, and the branches die.
Dead branches cause pests and diseases and reduce fruit set, so thin and prune moderately so that sunlight reaches the inside.
If the plant runs short of water while the fruit is growing, the fruit will drop.
Pests and diseases include melanose, citrus leafminer, scale insects, spider mites and aphids.
It is a food plant of swallowtail butterfly larvae.

[Notes]
The Japanese name is a Ryukyuan dialect word.
"Shi" means sour, said to derive from the use of unripe fruit when bleaching bashofu (banana-fiber cloth).

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