Ginkgo (Ginkgo biloba; in Chinese »È§ö, pinyin romanization, yin xing), also known as the Maidenhair Tree after Adiantum, is a unique species of tree with no close living relatives. The ginkgo is classified in its own division, the Ginkgophyta, comprising the single class Ginkgoopsida, order Ginkgoales, family Ginkgoaceae, genus Ginkgo and is the only extant species within this group. It is one of the best-known examples of a living fossil, because Ginkgoales other than G. biloba are not known from the fossil record after the Pliocene.
For centuries it was thought to be extinct in the wild, but is now known to grow in at least two small areas in Zhejiang province in Eastern China, in the Tian Mu Shan Reserve. However, recent studies indicate high genetic uniformity among ginkgo trees from these areas, arguing against a natural origin of these populations and suggesting that the ginkgo trees in these areas may have been planted and preserved by Chinese monks over a period of about 1000 years. Whether native ginkgo populations still exist has not been demonstrated unequivocally and is therefore uncertain.
The relationship of Ginkgo to other plant groups remains uncertain. It has been placed loosely in the divisions Spermatophyta and Pinophyta, but no consensus has been reached. Since Ginkgo seeds are not protected by an ovary wall, it can morphologically be considered a gymnosperm. The apricot-like structures produced by female ginkgo trees are technically not fruits, but are seeds that have a shell that consists of a soft and fleshy section (the sarcotesta), and a hard section (the sclerotesta).
Extracts of Ginkgo leaves contain flavonoid glycosides and terpenoids (ginkgolides, bilobalides) and have been used pharmaceutically. Ginkgo supplements are usually taken in the range of 40¡V200 mg per day.