Gallnuts (or nutgalls) are pathological excrescences formed on young branches or twigs of plants, induced by insect attacks, as a result of deposition of the eggs (Figure 60.1). The larvae pass through the pupa stage in gallnuts. The maturating insect emerges, and leaves the gallnut by boring a hole. There are two significant gallnuts as a source of tannin (gallotannin): Turkish gallnuts (Gallae Turcicae) and Chinese gallnuts (Gallae Chinensis).
Turkish gallnuts are formed on Quercus infectoria Oliv. (Fagaceae) by the gall wasp, Cynips gallae-tinctoriae Oliv. These gallnuts are usually referred to as "gallnuts of Q. infectoria" in the literature. Q. infectoria is a small tree or shrub, native to and distributed throughout Turkey, Greece, Iran, and Syria. The gallnuts from Q. infectoria are about 1—2.5 cm in diameter, being almost spherical in shape, with quite a smooth surface that is tuberculated on the upper part. They can be dark bluish-green, olive green, or white-brown in color.
Chinese gallnuts are formed on several Rhus species, mainly Rhus chinensis Mill. (Anacardiaceae), by different species of gallnut aphids, particularly the Chinese sumac aphid, Schlechtendalia chinensis Bell. The aphid parasitizes the leaves or petioles of the plant. R. chinensis is native to and distributed in areas of East Asia, including China (mainly the southern provinces), Malaysia, Indochina, Japan, and Sumatra. Chinese gallnuts are approximately 4—5 x 1.5 cm in diameter, horned, and reddish-brown in color, covered with velvety down. These gallnuts are usually harvested in the autumn after removal of the larvae.
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