Vachell’s stolen valour?
Published 21 November 2023

In the recent annals of botanical nomenclature, perhaps no genus has been the subject of more controversy, has raised more vitriol and ire, than the subject of this post. This is a genus whose question of identity escaped the marble halls of academia, sparked fiery condemnations in the public media, and inspired strident accusations of ‘taxonomic imperialism’. After sixteen years that I have been writing these posts, it’s finally time to consider what we talk about when we talk about Acacia.

Thorny acacia Vachellia nilotica, copyright Arthur Chapman.

Until a few decades ago, Acacia was generally recognized as a mega-diverse genus of over 1200 species, with species found in warmer regions of Africa, Asia, Australia and the Americas. However, as with so many other such taxa, the advent of molecular phylogeny revealed the genus’ polyphyly (Kyalangalilwa et al. 2013). As such, moves were made towards dividing it up, beginning with Leslie Pedley in 1986. The bulk of the old ‘Acacia’ could be divided between three clades. Two of these were widespread in Africa, Asia and the Americas; the third comprised most of the Australian species. As the effective type species was the African A. nilotica, the two pantropical clades became the genera Acacia and Senegalia while the oldest available name for the Australian clade was Racosperma.

The problem, as some saw it, was that the Australian clade was by far the largest of the three. Close to 1000 species belonged to this clade, including many familiar and well-publicised taxa. To bypass having to recombine so many names with the all-but-unused Racosperma, Orchard & Maslin (2003) submitted a proposal to switch the type species of Acacia from A. nilotica to A. penninervis, an Australian species. This proposal was supported by the Nomenclature Committee for Spermatophyta in 2004, albeit by the slimmest of margins (nine votes to six). And that’s when things started to get really messy.

The sun rises on an umbrella thorn acacia Vachellia tortilis, copyright Diana Robinson.

Even before Orchard & Maslin submitted their proposal for re-typification, Australian media had reacted negatively to the idea that the familiar Acacia would be superseded by the barbarous Racosperma (Robin & Carrathers 2012). This reached an apotheosis in 2005 when a radio broadcast on the topic lead to a flood of letters from the public to the Nomenclature Committee, including from garden societies and government representatives. One letter from a member of the public apparently threatened to make a formal complaint to the Federal Government if the name was allowed to be changed, which I can only describe as a particularly Australian way of approaching things.

Many of my readers more familiar with the politics of zoological nomenclature will doubtless be having Drosophilia flashbacks about now, and there are certainly parallels between the two cases. There are also some noteworthy differences. The public dialogue around Drosophila was largely focused on the status of one particular species, the genetic workhorse Drosophila melanogaster. In the case of Acacia, there was no one particular species with quite that prominence, but the overall pool of well-known species directly implicated was arguably larger. There were also major differences in procedure. In zoological nomenclature, though members of the public may make comments before a decision is reached, the ultimate decision on a proposal belongs to the Commission alone. In botanical nomenclature, the Nomenclature Committees make a recommendation on whether they think a proposal should be supported, and then a vote on whether to accept the Committees’ recommendations is held at the subsequent International Botanical Congress. The session in which this ratifying vote is conducted is open to members of the public—at least, members of the public who have paid to attend the Congress. Any decisions of this session are recorded in a new edition of the botanical Code of Nomenclature, and finally become permanent when the revised code is ratified at the following Congress.

Karroo thorn Vachellia karroo, copyright Arthur Chapman. The presence of paired stipular spines, together with inflorescence involucres, distinguishes Vachellia from Senegalia and Acacia.

In most cases, this probably all sounds more complicated than it is in practice. Prior to the Acacia affair, Nomenclature Committee recommendations had been uniformly rubber-stamped by the Congress (Moore 2007). So when the Acacia recommendation received an almost unprecedented degree of pushback at the Botanical Congress in Vienna in 2005, it is perhaps not surprising that it should incite an accompanying degree of administrative confusion. Without wishing to dwell on the legalistic minutiae (not least because they as are deeply confusing to me as they apparently were to some Congress attendees), the vote at the Vienna Congress ended up 45% to 55% against recognising Acacia with an Australian type species (Moore 2007). Nevertheless, this was ruled as allowing the proposal’s passage, as failing to reach the 60% supermajority that had been deemed necessary to quash a Committee recommendation. Acacia sensu A. nilotica would then be referred to by its next most senior monikor, Vachellia (named for a Reverend George Harvey Vachell who collected plant specimens in China).

Needless to say, not everyone was happy with this turn of affairs. Accusations were levelled of mishandling of procedures, of attempts to impose minority rule. The decision also lead to criticisms from the African public, lauding the Acacia as a symbol of the African landscape and incensed that its identity might by ‘stolen’ by Australia. To some, it became cast as an example of international disdain towards African concerns; as one Botswanan correspondent declared, “Does the retyping of the genus not amount to yet another act of economic and cultural pillage of the Third World by the First?” (Robin & Carrathers 2012). Questions were raised whether votes might be skewed by economic considerations preventing interested parties from attending the Congress. Some also raised less emotive objections: Acacia sensu A. nilotica was more widespread than Acacia sensu A. penninervis (including species in Asia and the Americas, which had kind of been lost in the wash among the histrionics of the Africa vs Australia debate), and recognition of Vachellia required the recombination over 100 species—considerably less than Racosperma’s 1000 or so, yes, but still no small chunk of change.

Whistling thorn Vachellia drepanolobium, copyright Peter Prokosch. This species has the spine bases swollen and hollow, providing domatia for symbiotic ants.

In 2011, the Acacia question was effectively raised again when that year’s Botanical Congress, held in Melbourne, voted whether to ratify the modified nomenclatural code resulting from the Vienna Congress, including the listing of Acacia among the conserved names. Though debate remained heated, and questions of procedure raised once more, the modified code ended up passing by a vote of 68% to 32%. Further proposals were introduced in an attempt to mollify both sides of the Africa vs Australia divide, such as the recognition of a genus ‘Afroacacia’ in place of Vachellia or, most bizarrely of all, the recognition of two distinct genera as Acacia (Vachellia) and Acacia (Racosperma). These proposals were ultimately not supported.

And that is where things have largely come to rest. Acacia has continued to be used as the genus name for the Australian taxa. Vachellia and Senegalia seem to have gained broad usage in the scientific literature, though many more popular sources (such as field guides) continue to refer to the African taxa as ‘Acacia’. And, of course, it should be stressed that the scientific circumscription of the genus name ‘Acacia’ ultimately has no bearing on the usage of the vernacular name ‘acacia’. Perhaps the final word should be given to a Russian attendant of the 2011 Botanical Congress, Dmitry Geltman, as quoted by Robin & Carrathers (2012). “We have had dissatisfaction about decisions about names before”, he said, “but then time passes and everything is okay again”.


Kyalangalilwa, B., J. S. Boatwright, B. H. Daru, O. Maurin & M. van der Bank. 2013. Phylogenetic position and revised classification of Acacia s.l. (Fabaceae: Mimosoideae) in Africa, including new combinations in Vachellia and Senegalia. Botanical Journal of the Linnean Society 172: 500–523.

Moore, G. 2007. The handling of the proposal to conserve the name Acacia at the 17th International Botanical Congress—an attempt at minority rule. Bothalia 37 (1): 109–118.

Orchard, A. E., & B. R. Maslin. 2003. (1584) Proposal to conserve the name Acacia (Leguminosae: Mimosoideae) with a conserved type. Taxon 52: 362–363.

Robin, L., & J. Carruthers. 2012. National identity and international science: the case of Acacia. Historical Records of Australian Science 23: 34–54.

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