Earliest Fossil Record of Asclepiadoideae (Dogbane Family) Reported from Asia

Scientists from the Chinese Academy of Sciences, writing in the academic journal “The American Journal of Botany”, have reported the earliest fossil record of the Apocynaceae family of plants from fossils found on the Central Qinghai‐Tibetan Plateau.  These flowering plants are often referred to as the “Dogbane” family, as many species have poisonous sap and this was used to keep dogs at bay.

The fossils representing preserved seeds collected from an altitude of around 4,800 metres indicate that during the Early Eocene, this part of Asia had a very much warmer subtropical climate.  Based on the seed fossils the researchers discovered, the scientists have been able to erect a new genus (Asclepiadospermum) and place two new species of Early Eocene plants within it (A. marginatum and A. ellipticum)

Fossilised Seeds of One of the Newly Described “Dogbane” Species Asclepiadospermum marginatum

Asclepiadospermum marginatum fossil seeds from Tibet.

Asclepiadospermum marginatum fossil seeds from a Tibetan plateau.

Picture Credit: Cédric Del Rio et al (The American Journal of Botany)

Asclepiadoideae is now geographically widespread, found tropical and subtropical regions around the world with something like 5,000 individual species recorded, ranging in size from trees to small shrubs and climbing vines.  Fossilised remains of these types of plants from the Neogene of Europe and North America are relatively abundant, but fossils from Asia are exceptionally rare.  The researchers studied three Apocynaceae seed impressions from the Lower Eocene Niubao Formation, Jianglang village, Bangor County on the central Qinghai‐Tibetan Plateau.  The fossilised remains are more than fifty million years old.

A Record of a Subtropical Ecosystem

After comparing with modern seeds and mapping of the seed characters on a phylogeny of the family Apocynaceae, the researchers recognised the fossils as part of the subfamily Asclepiadoideae and erected the new genus with its two species of prehistoric plants.  The Jianglang location is now situated at an altitude of approximately 4,800 metres above sea level and hosts cold alpine vegetation dominated by grassland.  However, these fossils indicate that the early Eocene climate and biodiversity were profoundly different.  Asclepiadoideae is now present in Asia and widespread in tropical to subtropical areas.

Commenting on the significance of the seed fossils, Professor SU Tao ( Laboratory of Tropical Forest Ecology, Chinese Academy of Sciences), corresponding author for the research paper, stated:

“The newly discovered early Eocene Asclepiadospermum from the central Qinghai‐Tibetan Plateau clearly belongs to Asclepiadoideae.  Our discoveries thus reconcile the fossil record and molecular estimations and represent the earliest fossil record for the subfamily.  Our fossils are important in documenting the floristic connection between Africa and Eurasia during the Eocene.  Based on current knowledge, Asclepiadospermum could represent an example of early diversification of Apocynaceae in Asia, with subsequent diversification in the Northern Hemisphere.”

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