Ginkgo biloba is often referred to as a "living fossil". Ginkgo leaves are common fossils in Jurassic and Cretaceous sediments of the Northern Hemisphere. The Ginkgo family (Ginkgoaceae) was thought to be extinct in the wild. In 1956 a small population of Ginkgo biloba was discovered in southeast China. The Ginkgo tree has been cultivated in the sacred gardens of China for centuries. Ginkgo has been planted worldwide and is valued for its beauty and medicinal properties (Kenrick & Davis, 2004, p. 148). Although Ginkgo biloba is referred to as a "living fossil", the fossil leaves of Ginkgo species show great variation in leaf morphology (Willis & McElwain, 2002, p. 139). The fossil wood and reproductive structures are rare as fossils. Ginkgo wood is prone to early decay.

Ginkgo Characteristics

In general, Ginkgo leaves are fan-shaped and may be deeply lobed (notched) to unlobed (entire). The veins appear to be parallel, but actually exhibit open dichotomous venation (each vein divides). Ginkgo biloba is a deciduous tree. The large numbers of Ginkgo leaves in the fossil record suggests that the ancestors of Ginkgo biloba were also deciduous.

Ginkgo biloba is dioecious (separate male and female trees). Male trees have stalked pollen sacs that are clustered together at the base of leaves. Female trees have pairs of unprotected ovules at the end of long stalks attached to the base of leaves. Ginkgo biloba is wind pollinated. Ovules are fertilized by free-swimming gametes. This fertilization process occurs on the tree. Ginkgo biloba and cycads are the only living seed plants that produce flagellated male gametes (Taylor, Taylor, and Krings, 2009, p. 744). One ovule gets pollinated and a fleshy false fruit forms over the seed. Butyric acid is produced by the false fruits after they drop to the ground producing a nasty smell. Landscape architects prefer to plant male Ginkgo trees for this reason.

Ginkgo trees have a constellation of characteristics, making their origin difficult to discern. The Ginkgo tree grows to 30 m. The vegetative structures of Ginkgo would remind one of a conifer or cordaite. The stem is a eustele with large amounts of wood (secondary xylem). Ginkgo wood is very conifer-like; however, in cross-section the tracheids are highly variable in size, which somewhat disrupts the radial arrangement (see micrograph below). Ginkgo also has large parenchyma cells scattered among the tracheids. Conifer tracheids in cross-section are of equal size, except for growth rings and exhibit an orderly radial arrangement. The leaves remind one of a deciduous flowering plant. The reproductive structures of the Ginkgo are more like that of a cycad.

A Change in the Flora

The diversification of Ginkgophytes during the Mesozoic helps to mark a significant change in the world's flora. Paleozoic flora was dominated by ferns and clubmosses (Paleophytic flora). The Paleophytic flora gave way to a Mesophytic flora during the Triassic period. Woody seed-bearing plants and their relatives dominated Mesophytic flora. Thus, the change from Paleophytic to Mesophytic represented a change in reproductive strategy; from spore producers to seed producers. Conifers, cycads, and ginkgos diversified during this time and dominated the landscape (Kenrick & Davis, 2004, p. 143).

Science Olympiad Fossil Event

The 2016 Science Olympiad Fossil List includes the genus Ginkgo within the phylum Ginkgophyta. Gymnosperms ("naked-seeds") include plants that usually bear their seeds in cone-like structures as opposed to the angiosperms (flowering plants) that have seeds enclosed in an ovary. Gymnosperms include the following extant divisions: Pinophyta, Ginkgophyta, Cycadophyta, and Gnetopyta.

Kenrick, P. and Davis, P. (2004). Fossil Plants. Smithsonian Books: Washington.

Taylor, T.N., Taylor E.L. & Krings, M. (2009). Paleobotany: The Biology and Evolution of Fossil Plants [2nd Ed]. New York: Academic Press.

Tidwell, W.D. (1998). Common Fossil Plants of Western North America. [2nd Ed]. Washington: Smithsonian Institution Press.

Willis, K.J. & McElwain, J.C. (2002). The Evolution of Plants. New York: Oxford University Press.