The Maidenhair Tree, Ginkgo biloba, is the last surviving remnant of a group of non-flowering seed plants (phylum Ginkgophyta) that way back in the Mesozoic had a worldwide distribution and were represented by multiple genera and species. Ginkgo came to the attention of European botanists in 1690, via cultivated trees in Japan, though it seems that the original home of G. biloba was the mountains of southwestern China. It is debatable whether truly wild populations of Ginkgo trees even exist anymore, but through cultivation the Ginkgophyta have regained shades of the ubiquity that they had in the age of the dinosaurs.
Ginkgo is a classic example of what are sometimes called “living fossils,” a lone hanger-on from a group that was far more diverse, widespread and ecologically important in the distant past, as revealed by the fossil record. The genus Ginkgo itself is known from the upper Triassic (200 million years ago) onward, with some fossils being quite similar, at least in form, to the modern Maidenhair Tree.
The term “living fossil” bothers me, though. Present day ginkgos aren’t identical to the fossils, and many of the ancient ginkgophytes don’t resemble the modern street tree in the slightest, unless viewed by someone with a background in paleobotany and plant morphology. The basic workings of genetics imply that it is essentially impossible for a real world population to remain genetically static from one generation to the next, let alone for millions of generations. So, Gingko biloba is certainly not a literal living fossil, untouched by the passage of time.
Even non-literal applications of “living fossil” are problematic. Ginkgos qualify as living fossils in large part simply because there weren’t that many of them around before people took them into cultivation, and they were confined to one obscure corner of eastern Eurasia. If it so happened that thousands of species of Ginkgophyta had survived into the present, and they grew in every forest, savannah, patch of desert scrub and vacant lot north of Antarctica, nobody would call them living fossils, never mind that they bore similarities to certain fossil remains.
Old Ginkgo tree at Washinomiya Shrine, Saitama, Japan. This individual has been coppiced: the original trunk was cut, and the tree is resprouting with multiple stems.
In our world, the Ginkgophyta barely squeaked by into the present, and another group of seed plants, the Magnoliophyta or flowering plants, diversified and came to dominate most terrestrial ecosystems. The designation of Ginkgo as a living fossil, and magnoliophytes—for example, petunias—as just ordinary plants, is purely retroactive and largely arbitrary: flowering plants, after all, have a fossil record that extends well back into the Mesozoic. Flowering plants share a common ancestor with Ginkgo, and the two lineages have been evolving for exactly the same amount of time since they diverged. A living fossil is more a matter of perception and lack of familiarity, than anything inherent in the plant.
In some alternate reality where pernicious ginkgophyte weeds infest suburban gardens of edible tomato-like ginkgophytes, and the only flowering plant that has dodged extinction is one species of petunia growing in a remote valley in Peru, perceptions would be different. Ginkgo biloba would be just another street tree, and petunias would be living fossils, a rare and freakish survival from a vanished world.
Reference: Gifford, E.M. & A.S. Foster. 1989. The Morphology and Evolution of Vascular Plants, Third Edition. W.H. Freeman and Co., New York.