Although tannins occur throughout the greater part of the vegetable kingdom, they are more prevalent among the Angiosperms, or higher plants, especially in certain Dicotyledon families, than they are among the lower types, such as fungi, algae, etc. The Gymnosperms also have classes in which tanning is well developed, e.g., the pines, spruces and hemlocks. Tannin may occur in almost any part of a plant, including roots, stems or trunk, hark, leaves, fruit, and even hairs. It may also be present in latex vessels and lactiferous tissue accompanied by other substances. In the living plant, tannin is present chiefly in solution in the vacuoles.
Tannins often occur in green or immature fruits, the quantity decreasing as the fruit ripens.
Tannin is also quite prevalent in tissues as a result of pathological conditions, such as plant galls. The ancient Greeks and Romans were well versed in the art of vegetable tanning and evidence indicates that vegetable tannins were used in China many thousands of years ago.