Palaeobotany for Paleoartists II: Fossil Ginkgoales

Given the relative intests in my post on the paleaortistic representation of the fossil Cycadales, I have decided to write an extremely small post about the paleoartistic representation of another fan favourite: Ginkgo and its fossil relatives.

Though many beautiful representations exist of this charismatic tree and some of its fossil relatives (helped by their presence in sites with dinosaurs and other paleoart darlings), and many reconstructions have been published in the scientific literature (see the Extinct Plant Paleoart database for examples), even some of the best and more accurate paleoartists can get some crucial aspects wrong. I will be focusing mostly on vegetative traits, since aspect of the reproductive morphology have been already treated by Maija Karala.

Extant ginkgoales include a single relict species, Ginkgo biloba. Even if this species is extinct in the wild, it is commonly found around the world as an ornamental tree.

The most unique characteristic of Ginkgo (and the one that is best represented in paleoart) is the shape of its leaves. They are fan-shaped, with a large amount of interspecific (and individual) variability between entire margins and highly dissected forms. Usually, two lobes are clearly recognisable. This is due to the fact that leaves are innervated by two veins entering the petiole, that then bifurcate multiple times thus forming two separate vein systems.

Another characteristic of modern Ginkgo is the architecture of the whole tree, which is driven by the two processes of rhythmic growth and differential orientation of the growh of stems. Young individuals have a single trunk that grows upwards, and a series of branches emerging at regular intervals that grows at a ~90% angle to the main trunk (plagiotropic branches), and tend to bend upwards only later in their life. This gives the tree an aspect not dissimilar to a christmas tree, which is more notable in young trees. Older trees might however have a much more complex appearance.

Schematic reconstruction of the architecture of Ginkgo biloba
Young ginkgo of the parc de l’Aulnaye. Souce Wikipedia.

Another very important characteristic of Ginkgo is the presence of two types of branches. So called “long shoots”, with extended internodes, expand the canopy, while “short shoots” with compressed internodes bear most of the leaves as well as the axillary reproductive structures. This is true for young trees as well as older trees. Some times, a long shoot is produced from the apex of a short shoot. A similar shoot dimorphisms is present in some conifers such as larches and cedars.

Fossil ginkgoales include both close relatives of Ginkgo as well as more “odd” relatives such as leaves assigned to Baiera, Sphenobaiera, Czekanowskia, which present varying degree of dissection and elongation. However, even these relatives had similar characteristics to extant Ginkgo. Their leaves have a basically bilobed plan, even though this might be confounded by extreme dissection and elongation of the lobes. Also, there is evidence that these leaves were brought on short shoots.

A reconstruction of the plant bearing Membranifolia admirabilis with most of the characteristics of Ginkgoales: Short shoots and long shoots, most leaves born on short shoots, and leaves with a general bilobate framework. Source Wikipedia, attribution S. Fernandez

Additional references:

The wikipedia page for Ginkgo biloba has a surprising amount of good information.

This extremely interesting experiment on how leaves of Sphenobaiera and Czekanowskia should look like.

Bauer, K., Kustatscher, E. and Krings, M., 2013. The ginkgophytes from the German Kupferschiefer (Permian), with considerations on the taxonomic history and use of Baiera and Sphenobaiera. Bulletin of Geosciences, 88(3), pp.539-556.

Little, S.A., Jacobs, B., McKechnie, S.J., Cooper, R.L., Christianson, M.L. and Jernstedt, J.A., 2013. Branch architecture in Ginkgo biloba: Wood anatomy and long shoot–short shoot interactions. American journal of botany, 100(10), pp.1923-1935.

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