The Acacia wars, resolved

In an at times acrimonious process (some have even called it a “wattle war”), the former plant genus Acacia has been split into five genera, with further splits likely. The XVIII International Botanical Congress in 2011 confirmed a previous decision to retain the Acacia name for the largest of the resulting genera, found mainly in Australia:

“Under the internationally accepted rules governing the correct naming of plants, the International Code of Botanical Nomenclature, the name would normally have remained with the African-American group, as this includes the species Acacia nilotica, which is the nomenclatural type species… However, a special provision of the Code allows for the name of the type species of a genus to be changed in cases like this, where strict application of the rules would require a large number of species to be renamed… An application under this provision was made in 2003… This was considered by the relevant botanical committees, who decided in its favour. The International Botanical Congress at Vienna in 2005 ratified this decision. The Vienna decision was contested by a group of botanists involved with African and American acacias. The Melbourne Congress, in two important votes on the first day of the Nomenclature Section, supported the procedure used in Vienna by a large majority. Support for this decision was widespread and not confined to Australian delegates. This vote effectively confirmed that the type species of Acacia is now an Australian species.”

The resulting division of the former Acacia is as follows:

The map below shows the distribution of the new genera, divided into the Americas, Africa, Asia, and Australia & the Pacific (background image from NASA Visible Earth). A degree of reorganisation was going to be needed whatever nomenclature proposal was accepted, but it certainly made sense to retain the Acacia name for 71% of the original species (although Wikipedia, which becomes more and more partisan as time passes, ran a campaign against the official decision for several years). The botanical community seems quite happy using the new names, and it does not seem that the issue will resurface at the XIX International Botanical Congress later this year, although there continues to be debate about how to resolve similar issues in the future.

Here are the five new genera, with examples:

Mariosousa

About 13 species, in the Americas. See theplantlist.org.


Mariosousa willardiana (Palo Blanco – photo: Tomas Castelazo)

Acaciella

About 15 species, in the Americas. See theplantlist.org.


Acaciella angustissima (photo: USDA)

Vachellia

About 163 species, throughout the tropics. See theplantlist.org.


Vachellia smallii (photo: Stan Shebs)

Senegalia

About 203 species, throughout the tropics. See theplantlist.org. This genus is likely to be split further.


Senegalia laeta (photo: Marco Schmidt)

Acacia

About 987 species, almost all in Australia and the Pacific.


Acacia pycnantha (Golden Wattle – photo: Melburnian)


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