**1.1.** *Vachellia* **split from the** *Acacia* **genus**

Until 2005, *V. karroo* was known as *Acacia karroo,* but according to recent taxonomic research and molecular evidence, the *Acacia* genus was shown to be polyphyletic [7]. It could not be maintained as a single entity, and a proposal was put forward for it to be divided into five genera [8–10]. According to the new proposed classification, ratified at the International Botanical Congress in Vienna in July 2005, *Acacia* genus was split into five monophyletic genera, with all the African *Acacia* now falling under *Vachellia* and *Senegalia* as follows:


There were objections toward preserving the name *Acacia* for the Australian and other related species [11], but the decision taken in Vienna in 2005 was finalised at the next International Botanical Congress held in Melbourne in 2011. Before the split, there was a total of 40 *Acacia* species, subspecies and varieties represented in South Africa [1]. The split has now resulted in 23 species, subspecies and varieties of *Vachellia* and 17 of *Senegalia* (**Table 1**). The key diagnostic character distinguishing *Vachellia* from *Senegalia* is the presence of stipular spines in *Vachellia*, while *Senegalia* may have prickles but always lack stipular spines [12].


distribution [3]. The species are a prominent feature in the Savanna biome (bushveld) in South Africa but can also form local dominant stands in other biomes such as the Grassland and Nama-Karoo biomes. Those with a broad distribution range, like *V. karroo*,

The *Vachellia* species are pod-bearing woody plants that range from shrubs to large trees. They can be sprawling or climbing, and this character differs with habitat [4]. This genus in Africa is readily recognised by its thorns, which are typically paired and straight. These thorns are modified stipules, which become hard and spiny [1, 5] and are important for identification of the trees [6]. *Vachellia* trees can further be distinguished by their characteristic growth form, by bark, and also by pods. This is however a taxonomically difficult genus containing a number of closely related species whose recognition and identification are not

Until 2005, *V. karroo* was known as *Acacia karroo,* but according to recent taxonomic research and molecular evidence, the *Acacia* genus was shown to be polyphyletic [7]. It could not be maintained as a single entity, and a proposal was put forward for it to be divided into five genera [8–10]. According to the new proposed classification, ratified at the International Botanical Congress in Vienna in July 2005, *Acacia* genus was split into five monophyletic genera, with all

(i) *Acacia*, preserved for more than 960 largely Australian species, which all belonged to the

(ii) *Vachellia*, former sub-genus *Acacia*, approximately 161 pantropical species (Africa, Asia

(iii) *Senegalia*, former sub-genus *Aculeiferum*, with 203 pantropical species (Africa, Asia and

(iv) *Acaciella*, former sub-genus *Aculeiferum* section *Filicinae*, contains 15 species from the

There were objections toward preserving the name *Acacia* for the Australian and other related species [11], but the decision taken in Vienna in 2005 was finalised at the next International Botanical Congress held in Melbourne in 2011. Before the split, there was a total of 40 *Acacia* species, subspecies and varieties represented in South Africa [1]. The split has now resulted in 23 species, subspecies and varieties of *Vachellia* and 17 of *Senegalia* (**Table 1**). The key diagnostic character distinguishing *Vachellia* from *Senegalia* is the presence of stipular spines in *Vachellia*, while *Senegalia* may have prickles but always lack stipu-

the African *Acacia* now falling under *Vachellia* and *Senegalia* as follows:

(v) A yet unnamed genus with 13 species from the Americas.

occur in several biomes [1].

110 Pure and Applied Biogeography

always simple [3, 5].

**1.1.** *Vachellia* **split from the** *Acacia* **genus**

former sub-genus *Phyllodineae*.

and Latin America).

Latin America).

Americas.

lar spines [12].

**Table 1.** South African *Vachellias (Acacias*) and their new name combinations [1, 12, 13].
