Ginkgo: the immortal, binary tree

The ginkgo tree in the lower Dunedin Botanic Garden beside the tulip tree and adjacent to the Visitor Centre is currently a magnificent spectacle, its golden autumn leaves are well worth seeing. Ginkgo biloba – a living fossil – is one of the oldest extant seed plants. It is a gymnosperm, and the only living species in the Order Ginkgoales, which first appeared over 290 million years ago. The genus Ginkgo dates to the Middle-Jurassic epoch, about 170 million years ago. With a long history of human cultivation in East Asia, ginkgo trees are remarkable and unique. All veins in their fanshaped leaves radiate out from the leafbase, never forming a network. Ginkgo biloba trees are either male or female. Male trees have small pollen cones, while females bear 1.5cm–2cm long fruitlike structures which contain seeds. These fruits produce butyric acid, which smells like rancid butter when they fall. Remarkably, ginkgo seeds are fertilised by motile sperm, as are cycads, ferns, mosses and algae, unlike other seed trees. The large, 70 microns to 90 micronslong sperm are propelled by several thousand flagella. Two sperm are produced, one fertilising the ovum. Fertilisation of ginkgo seeds occurs just before or after they fall.

Ginkgo trees are very hardy and resistant to both disease and attack by insects and other invertebrates. Aerial roots occur as a survival technique. Some trees are claimed to be over 2500 years old. A Chinese study in 2020 found ginkgo trees up to 667 years old showed little genetic effects of ageing and continued to make phytochemicals indefinitely.

Fruit body on female ginkgo tree.

Fossils clearly related to modern ginkgo date to the Permian, over 290 million years ago. These had motile sperm, like the single modern species.

Ginkgo, associated with Buddhism and Confucianism, has long been cultivated in China and Japan, where some trees in temple gardens are over five hundred years old. It is resistant to pollution and is one of the few plants that can survive in the

centres of big modern cities. Ginkgo trees even survived the nuclear blast in Hiroshima. Although initially charred, they soon became healthy.

PHOTO: JEN COPEDO Leaves from ginkgo beside tulip tree in lower Botanic Garden.

PHOTOS: SUPPLIED One of a pair of huge sperm produced by a pollen tube that grew from a pollen grain from a male ginkgo tree. The sperm is swimming by means of many flagella to eggs contained within the future seed. This happens in the fruit bodies on the female ginkgo tree, or shortly after they fall to the ground.