**1.2. Morphological variation of** *V. karroo*

The species displays considerable variation in its appearance, size and other characters [3, 14]. This variation in *V. karroo* is seemingly regional with plants from different geographical areas appearing distinctly different with regard to one or more features [1, 13, 15]. The "typical" form of *V. karroo* grows in the Karoo, Free State, KwaZulu-Natal, and some northern parts of the country [1]. It is a small to medium-sized tree commonly growing to 5–12 m in height but may become a very large tree of up to 22 m on river banks or in other favourable conditions [1, 2]. The tree is usually single-stemmed though sometimes multi-stemmed, branching high above the ground to give a rounded crown (**Figure 1**).

The typical *V. karroo* has a rough, longitudinally fissured bark which is dark on the trunk (**Figure 2A**) and main branches but rusty red in younger branches (**Figure 2B**). The foliage is generally dense and comprises dark green compound leaves (**Figure 2C**). Inflorescences are balls of small sweetly scented yellow flowers (**Figure 2D**), while the pods are flat, mostly sickle shaped with minor constrictions between seeds and dehiscent (**Figure 2E**). The thorns are long, paired, straight, and shining white (**Figure 2F**) and indicate an adaptation of *V. karroo* to its environment because of their protective function [2]. They are larger and abundant on the lower branches that are within reach of animals (and also on young trees) (**Figure 3**) but fewer on the higher parts of larger (and old) trees [2, 4].

**Figure 1.** A *Vachellia karroo* tree near Bloemfontein, South Africa (photo: M. Dingaan).

**1.2. Morphological variation of** *V. karroo*

112 Pure and Applied Biogeography

above the ground to give a rounded crown (**Figure 1**).

fewer on the higher parts of larger (and old) trees [2, 4].

**Figure 1.** A *Vachellia karroo* tree near Bloemfontein, South Africa (photo: M. Dingaan).

The species displays considerable variation in its appearance, size and other characters [3, 14]. This variation in *V. karroo* is seemingly regional with plants from different geographical areas appearing distinctly different with regard to one or more features [1, 13, 15]. The "typical" form of *V. karroo* grows in the Karoo, Free State, KwaZulu-Natal, and some northern parts of the country [1]. It is a small to medium-sized tree commonly growing to 5–12 m in height but may become a very large tree of up to 22 m on river banks or in other favourable conditions [1, 2]. The tree is usually single-stemmed though sometimes multi-stemmed, branching high

The typical *V. karroo* has a rough, longitudinally fissured bark which is dark on the trunk (**Figure 2A**) and main branches but rusty red in younger branches (**Figure 2B**). The foliage is generally dense and comprises dark green compound leaves (**Figure 2C**). Inflorescences are balls of small sweetly scented yellow flowers (**Figure 2D**), while the pods are flat, mostly sickle shaped with minor constrictions between seeds and dehiscent (**Figure 2E**). The thorns are long, paired, straight, and shining white (**Figure 2F**) and indicate an adaptation of *V. karroo* to its environment because of their protective function [2]. They are larger and abundant on the lower branches that are within reach of animals (and also on young trees) (**Figure 3**) but

**Figure 2.** *Vachellia karroo* trunk (A), branches (B), leaves (C), flowers (D), pods (E) and thorns (F) (photos: M. Dingaan).

Due to the extreme variation in *V. karroo* form, many of the variations have been described as different species in the past, resulting in numerous synonyms. The differences in form have thus been considered by some botanists to be distinct enough to warrant division of the species into sub-species or at least varieties or even to again regard some forms as different species altogether. Ross [13] concluded that it would be preferable to regard *V. karroo*

**Figure 3.** A young *Vachellia karroo* tree, splendidly armoured with long white thorns (photo: M. Dingaan).


**Table 2.** The *Vachellia karroo* complex.

as a variable polymorphic species rather than to divide the species into a number of infraspecific taxa. Regardless, the *V. karroo* complex has recently been split, with some authors recognising the following as distinct species (**Table 2**): *V. natalitia*, *V. dyeri*, *V. kosiensis* [5, 16] and *V. theronii* (previously published incorrectly as *V. montana,* i.e., an invalid name) [17]. Coates Palgrave [5] further recognises *V. robbertsei* as a species that could have evolved from *V. karroo* and *V. gerrardii* genes. The locations where these different forms (previously) recognised within the *V. karroo* complex occur are shown in **Figure 4**.

**Figure 4.** Map indicating occurrences of the various morphological variations (described in **Table 2**) within the *Vachellia karroo* complex. Note: The three provinces labelled in italics indicate occurrence of variation 1.
