R is for……. Rhoiptelea chiliantha

Rhoiptelea chiliantha used to be in its own family, the Rhoipteleaceae, until the Angiosperm Phylogeny Group moved it into the Juglandaceae in their review in 2009 (APG III). This review immediately made it the oldest of the walnuts.

The only member of the monotypic genus Rhoiptelea, the ‘Horsetail’ tree is listed as vulnerable on the IUCN Redlist. Growing in Southern China and across the border into Vietnam the tree is found only singly or in small groups. However it is also a re-coloniser of cleared ground and thus the Cardamom plantations that are encroaching on its forest habitat also provide this species with an opportunity. Alas seedling mortality is high  and thus the re-population of cleared areas does not compete with the clearing itself.

Its fossil history places it securely in the latest Cretaceous and proves that the genus at least had a much wider distribution than it currently boasts. Fossilised pollen grains that are assigned to the genus Plicapollis from the Late Cretaceous are very similar to the pollen of Rhoiptelea and there are also pollen fossils that are actually assigned to Rhoiptelea from the Maastrichtian (the very latest stage of the Cretaceous) of North America. There is a macro-fossil record of fossilised fruit that has been assigned to Rhoiptelea from the Maastrichtian of Europe too but alas these seeds have few identifiable characteristics and thus their relationship to the Rhoipteleaceae needs to be reviewed.

Here in the ‘Fossil’ garden we have a plant of Rhoiptelea chiliantha which, on receiving it from a good friend, soon became a favorite tree. Little grown and very little known this species truly deserves to be more widely appreciated for its wonderful multi-pinnate leaves, with their winged petioles, that emerge the deepest red in the spring.