Sour Orange (Citrus Aurantium), also known as bitter orange, Seville orange, bigarade orange or marmalade orange, is an evergreen, spiny tree that grows up to 9 m high by 6 m wide, having a compact, rounded top. It is hardy to zone 9 and is frost tender, yet it can stand several degrees of frost for short periods. Dormant plants can withstand temperatures down to about -6 Celsius degrees (21 F) so long as this is preceded by cool weather in order to harden off the plant. The young growth in spring, even on mature plants, is frost-tender and so it is best to grow the plants in a position sheltered from the early morning sun.
It has smooth, brown bark, green twigs, angular when young and flexible, not very sharp and thorns of 2.5-8 cm long. It is in leaf all year, bearing ovate leaves that are fragrant when crushed. It flowers from mid spring to early summer. The hermaphrodite flowers are highly fragrant, borne singly or in small clusters in the leaf axils. The plant is self-fertile. The fruits are round, oblate or oblong-oval, orange or reddish-orange with a rind that is rough, strong scented and bitter. The fruits have 10-12 sections and the pulp is acid, containing from a few to numerous seeds.
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