Ginkgos are very large trees, normally reaching a height of 20–35 m (66-115 feet), with some specimens in China being over 50 m (164 feet). The tree has an angular crown and long, somewhat erratic branches, and is usually deep rooted and resistant to wind and snow damage. Young trees are often tall and slender, and sparsely branched; the crown becomes broader as the tree ages. During autumn, the leaves turn a bright yellow, then fall, sometimes within a short space of time (1–15 days). A combination of resistance to disease, insect-resistant wood and the ability to form aerial roots and sprouts makes ginkgos very long-lived, with some specimens claimed to be more than 2,500 years old: One of the oldest Ginkgo trees is in Shanghai, within the Yuyuan Garden; it is four centuries old. A 3,000 year-old ginkgo has been reported in Shandong province in China.^[5]

Some old Ginkgos produce aerial roots, known as chi chi (Japanese; "nipples") or zhong-ru (Mandarin Chinese), which form on the undersides of large branches and grow downwards. Chi chi growth is very slow, and may take hundreds of years to occur. The function, if any, of these thick aerial roots is unknown.

Leaves

The leaves are unique among seed plants, being fan-shaped with veins radiating out into the leaf blade, sometimes bifurcating (splitting) but never anastomosing to form a network.^[6] Two veins enter the leaf blade at the base and fork repeatedly in two; this is known as dichotomous venation. The leaves are usually 5-10 cm (2-4 inches), but sometimes up to 15 cm (6 inches) long. The old popular name "Maidenhair tree" is because the leaves resemble some of the pinnae of the Maidenhair fern Adiantum capillus-veneris.

Although Ginkgo biloba and other species of the genus were once widespread throughout the world, the tree currently occurs in the wild only in the northwest of Zhejiang province in the Tianmu Shan mountain reserve in eastern China, but even its status as a naturally occurring species there is questionable. In other areas of China it has been long cultivated and it is common in the southern third of the country. It has also been commonly cultivated in North America for over 200 years, but during that time it has never become significantly naturalised.

Culinary use

The nut-like gametophytes inside the seeds are particularly esteemed in Asia, and are a traditional Chinese food. Ginkgo nuts are used in congee, and are often served at special occasions such as weddings and the Chinese New Year (as part of the vegetarian dish called Buddha's delight). In Chinese culture, they are believed to have health benefits; some also consider them to have aphrodisiac qualities. Japanese cooks add Ginkgo seeds (called ginnan) to dishes such as chawanmushi, and cooked seeds are often eaten along with other dishes.

Medicinal uses

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 40–200 mg per day. Recently, careful clinical trials have shown Ginkgo to be ineffective in treating dementia or preventing the onset of Alzheimer's Disease in normal people