The ginkgo, the tree that lays eggs 🥚

By Catherine Lenne, Lecturer-Researcher in Plant Biology, Université Clermont Auvergne (UCA)

"The tree that survived Hiroshima," "prehistoric tree," "living fossil"... Ginkgo biloba has been given many labels, not always accurate, which overshadow one of its greatest peculiarities: its unparalleled sex life.


It's a tree that stands out in our parks and gardens. Its small bilobed leaves, which turn yellow in autumn, have a curious fan-shaped venation, unique among trees. They make it instantly recognizable: it's the Ginkgo biloba, an extraordinary tree that has long fascinated due to its many oddities.

A prehistoric tree?

The first peculiarity is significant: the ginkgo is unique on the planet! Belonging to a very ancient plant family, the Ginkgoales, which dates back 270 million years, it is the sole surviving representative today. Moreover, it closely resembles its long-extinct and fossilized cousins, so much so that it was long believed to have remained unchanged for millions of years, as if time and evolution had no hold on it. Darwin coined the term "living fossil" to describe such immutable beings, and today's media perpetuate this idea by calling the ginkgo a "prehistoric tree".


A misconception, of course, as the notion of a living fossil is nonsensical, since a fossil is by definition a dead organism whose organic structures have been preserved through mineralization. The ginkgo has indeed evolved like any living species, but this isn't immediately apparent. Scientifically speaking, this tree is a relict species, and its seemingly unchanged form over time is described as panchronic.

The tree that survived the atomic bomb, but not the only one

Secondly, the ginkgo has a reputation for being "indestructible." It is exceptionally resistant to diseases and pollution, and these extraordinary abilities help explain its longevity, easily exceeding 1000 years or more in its natural habitat. But it's not the only tree on the podium of those reaching canonical ages. The oak can also live for a millennium, the olive tree for several, and some Rocky Mountain pines (Bristlecone pines), born before the Egyptian pyramids, hold the world record for the oldest trees, certified at over 5800 years.

The ginkgo's reputation for immortality is bolstered by the fact that it survived the atomic bomb that obliterated Hiroshima on August 6, 1945. However, it is not the only tree that survived the apocalypse that day. About twenty other trees, such as ailanthus, willows, eucalyptus, catalpa, and others, even closer to the epicenter than the ginkgo, also revived, sprouting vigorous shoots from their charred stumps after the disaster. But oddly, popular memory has retained only the ginkgo.

This somewhat overblown "superhero" label ultimately obscures the real reasons why the ginkgo is truly a unique tree, and among them, its extraordinary sexuality. Unlike deciduous or coniferous trees, and akin to birds, the ginkgo is a tree that lays "eggs."

Male and female ginkgos

Its entire sex life is, in fact, highly original. First, because it is a dioecious species, meaning the sexes are separate. There are male ginkgos and female ginkgos. This is rather rare among trees (only 6% of flowering plants), even though this separation of sexes is not unique to the ginkgo, existing also in deciduous trees like poplars, willows, holly, etc., and in some conifers like yews. The general rule among trees is monoecy, where male and female sexes are carried by the same individual, in the form of cones in conifers or flowers in deciduous trees.


To recap, in these majority cases, the stamens present in male cones or flowers produce pollen grains that carry male sex cells (sperm) to the female organs. These are the ovules, sort of boxes containing and protecting female sex cells (oospheres), and they are carried by the scales of female cones or enclosed in the pistil of a flower. The sexual behavior of the ginkgo thus differs from that of the majority of other trees.

A naked ovule scented with butyric acid

Next, the ginkgo's sexual organs are rather unusual. The pollen-producing stamens are gathered in a kind of tiny spike called a catkin because it resembles a cat's tail. This organization is comparable to that of male cones in conifers or even the male flowers of many deciduous trees. Think, for example, of the golden, hanging catkins of willows or hazelnuts in spring. On the male side, then, the originality is minimal.

However, the female sexual organs are neither cones nor flowers, but huge yellow, fleshy balls, hanging at the end of long stalks like large mirabelle plums on a plum tree. In autumn, they fall to the ground and rot, releasing butyric acid with a strong, unpleasant odor, halfway between vomit and rancid butter. It's impossible to mistake the identity of a female ginkgo then; the identification is olfactory and unforgettable!


These stinky autumn balls are the "fruits" of the ginkgo, but this term is botanically incorrect. Because a fruit is the result of the transformation of a flower after fertilization, and since the ginkgo has no flowers, it cannot have fruits. The female ginkgo's ball is actually a simple but large ovule, "naked" because it is not protected by any structure, unlike the ovules of deciduous trees buried in the pistils of female flowers, or to some extent the ovules of conifers, carried by the scales of the female cone (the "pine cone"), tightly packed together when the cone is young.

Seeds that aren't quite seeds

Since it produces ovules, a structure that appeared about 350 million years ago, the ginkgo belongs to the group of Spermatophytes, also called seed plants, because fertilized ovules turn into seeds. The ginkgo is thus a tree that produces seeds, like all modern trees. So far, nothing particularly original, except that its seeds aren't quite seeds.

To be a true seed, four boxes must be checked. First, it must obviously contain an embryo, the future plant, resulting from the union of the two sex cells during fertilization: the sperm brought by the pollen grain and the oosphere, the female gamete of plants, nestled in the ovule.

Second, this embryo must be embedded in a nutrient tissue filled with carbon reserves that will fuel the early stages of its development during germination. These carbon reserves are only produced after fertilization, if and only if an embryo is formed.

Third, the seed is protected by a hard outer shell, and fourth, the whole is in a state of slowed life, a kind of sleep that allows germination to be delayed until environmental conditions are favorable for growth, i.e., the following spring in temperate climates (which allows the passage of the harsh winter season without issue).

But in the case of the ginkgo, not all four conditions are met, and its "seeds" are false; they are actually called "pre-seeds." What are they missing? If the ginkgo's ovules are so large, it's because they are filled with a large amount of nutrient reserves, but these accumulated long before fertilization. This represents a considerable energy expenditure for the ginkgo and a rather unprofitable investment, as not all these filled ovules will be fertilized, and the precious reserves will be lost when they fall in autumn. However, as they rot, they will enrich the soil at the base of the tree, which will ultimately nourish it later.

Thus, the ginkgo lays "eggs" quite analogous to those of a hen, whose reserves accumulate during transit in the genital tract, without any need for fertilization. These hen eggs are also rarely fertilized, unless the rooster has crossed paths with the hen in the barnyard. The ginkgo is indeed a strange bird, as it is somewhat oviparous!

Fertilization closer to that of algae

Finally, another oddity of the ginkgo's sexuality makes it a truly extraordinary tree... When fertilization occurs, the process remains archaic, closer to that of algae than to that of trees. Indeed, during the evolution of plants, the invention of aerial fertilization completely freed this crucial step from the presence of water, unlike the ancestral mode of fertilization in algae, mosses, and ferns.

In true aerial fertilization, that of conifers or deciduous trees, the sperm are not swimmers; they have lost their flagella, the kind of vibrating filament that allows them to move in water. They cannot therefore move to reach their female partner, the oosphere, in the ovule. They are instead brought right next to it by a siphon system formed by the germination of the pollen grain deposited on the cone or flowers. This pollen tube allows fertilization completely independent of external water, called siphonogamy.


But in the case of the ginkgo, which is nonetheless a tree adapted to the aerial environment, fertilization remains aquatic. The ovule is hollowed out with a pollen chamber filled with a liquid that overhangs the heads of the oospheres (diagram). In spring, pollen grains enter the still tiny ovule through a small hole, the micropyle, which beads a sticky drop of water that retracts inside. Pollen grains that have entered the ovule then germinate a short pollen tube that anchors in the wall of the chamber, and it is only a few weeks later that the grain releases its contents into the liquid: swimming sperm, equipped with vibrating cilia. They swim toward the oospheres at the bottom of the pool to unite with them.

The presence of water and swimming sperm is characteristic of aquatic fertilization or zooidogamy (from "zooid," swimming cell, and "gamy" = marriage), almost unique among trees or nearly... the cycads, plants with a palm-like appearance and close relatives of ginkgos, also have swimming sperm and aquatic fertilization!

Ultimately, this archaic mode of fertilization in the ginkgo, inherited from the distant past of plants born in the depths of the oceans, somewhat justifies its nickname of "prehistoric tree"!

This article is inspired by the chapter dedicated to the ginkgo in Vous avez dit biz'arbres ? by Catherine Lenne, published by Belin and dedicated to the astonishing and prodigious oddities that can be observed among trees.