Of all the tea family's plants, only a few actually contain caffeine
The tea family, Theaceae, includes showy camellias, American trees and the bush that gives us tea. Yet caffeine turns up only in one small section of Camellia, and the tea bush's high levels, 2.5 to 4 percent of dry leaf weight, are largely the product of human selection.
Theaceae is a family of shrubs and trees whose size depends on who is counting: anywhere from seven to 40 genera, according to how botanists draw the boundaries. A group once lumped in, Ternstroemiaceae, was moved to a separate family by the APG III classification of 2009. Most species come from China and East Asia, but relatives also grow in Malesia, tropical South America and the southeastern United States, where Franklinia is found nowhere else.
The leaves are simple, usually glossy and toothed, each tooth often capped by a small gland that falls away. Most genera keep their leaves all year, though Stewartia and Franklinia are deciduous. Flowers are typically large, pink or white and often strongly scented, packed with anywhere from 20 to over 100 stamens. An unusual feature is pseudopollen, grains produced not by the usual pollen cells but from connective tissue, marked with ribs or rings. A fossil flower about 91 million years old may belong here or to a neighbouring family.
Chemically the family shares tannin-like compounds such as ellagic acid, flavonols and saponins in seeds, leaves, wood and bark. Catechins and gallic acid, though, occur only in Camellia section Thea, which includes the tea plant, Camellia sinensis, and a couple of close relatives. Caffeine and its chemical precursors theobromine and theophylline are confined to that section too.
Several other camellias are brewed as drinks in parts of Asia, among them Camellia taliensis and Camellia irrawadiensis, while many species are planted in gardens for their handsome flowers and dark foliage. So the same family supplies both a global beverage and some of the most familiar ornamental shrubs.
Source: Theaceae
