The wonky spike-thorns

The Celastraceae is the fourth largest tree family in southern Africa, containing just less than 100 species (~94 species). Yet, despite a few notable and abundant species, the Celastraceae is “a rather indistinct family” according to the Field Guide to Trees of Southern Africa [1]. Fortunately, the guide goes on to add that as one becomes more familiar with the family you can start to recognise…

…a distinct, though difficult to describe, celastraceous ‘look’.

van Wyk and van Wyk [1]

So what might that look be? Well…the guide mentions that the leaves are simple and arranged spirally, or opposite, or clustered in fascicles… And when the leaves are opposite in the adult tree, they are often arranged alternately in the juvenile saplings of the same species. Indistinct indeed. The guide also mentions that the

young twigs tend to be greenish and somewhat angular…

…and that many species appear to have spines or spike-thorns (hence the popular name). Overall, I get the distinct impression that species of the Celastraceae are like tall, skinny people: somewhat edgy, a bit wonky and knobbly, and, most distinctly, all elbows and knees.

Gymnosporia and Maytenus

Unsurprisingly, the generic relationships within the Celastraceae family are still somewhat uncertain, including among two of the largest genera, Gymnosporia and Maytenus. The largest genus in southern Africa (Gymnosporia) did not exist until recently and is still in a state of “taxonomic flux”. Prior to the early 2000’s most of the species now contained within Gymnosporia were considered to be a part of Maytenus. Taxonomic investigations conducted by researchers at the University of Pretoria (most notably Marie Jordaan and colleagues) recognised Gymnosporia based on the presence of several “distinguishing” features, or, as I think of it, based on features pertaining to the classic celastraceous “look”. Gymnosporia can be recognised by the…

…truncated branchlets and spines, alternate leaves or fascicles of leaves, an inflorescence that forms a dichasium*, mostly unisexual flowers, and fruit forming a dehiscent capsule, with an aril on the seed.

So, the next time you find yourself in the field wondering what that common, knobbly, wonky spiny looking tree is, you can feel confident that it is a Gymnosporia (like this Gymnosporia heterophylla above). But if someone asks, best to call it a spike-thorn.

Tomorrow, we move on to cover one of my favourite families, the much more easily identifiable Euphorbiaceae!

Notes:

*A dichasium is a cyme where each flowering branch gives rise to two or more branches symmetrically.

[1] According to the Braam van Wyk and Piet van Wyk in the Field Guide to Tree of Southern Africa published by Struik Nature. This is an excellent guide and I would urge anyone interested in southern African trees to go out and purchase a copy.

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