五倍子 are galls produced on the leaves of
盐肤木 (Rhus chinensis, Chinese sumac) when the aphid Schlechtendalia chinensis lays eggs in them — the swelling can be up to five times the leaf's normal size, hence
五倍 ('five-fold'). Used since the Tang dynasty in TCM as
收敛 (astringent) and to staunch bleeding; also a major commercial source of tannic acid for ink, dye, and leather tanning.
