Theanine is derived from tea leaves. Tea is native to eastern Asia and is a member of the Theaceae family. This evergreen shrub or tree grows to over 9 m in height and is pruned from 60 cm to 1.5 m for cultivation. Its dark green, serrated-edged leaves are alternate and oval, while its white and fragrant blossoms appear singly or in clusters.
The chemical has also been isolated from the edible mushroom Boletus badius. The mushroom is commonly found in late summer and autumn in the United States, and is reddish brown to dark brick/brown in color with a 4 to 12 cm tall stem. The flesh is white to yellow in color, and becomes a light blue/green color when cut or bruised.