茶树
Theanine is found primarily in plant and fungal species. It was discovered as a constituent of tea ("Camellia sinensis)" in 1949, and in 1950 a laboratory in Kyoto successfully isolated it from gyokuro leaf, which has high theanine content. Theanine is substantially present in black, green, and white teas from "Camellia sinensis" in quantities of about 1% of the dry weight. Deliberately shading tea plants from direct sunlight, as is done for matcha and gyokuro green tea, increases L-theanine content. The -enantiomer is the form found in freshly prepared teas and some human dietary supplements.