Vachellia
Vachellia is a genus of flowering plants in the legume family, Fabaceae, commonly known as thorn trees or acacias. It belongs to the subfamily Mimosoideae. Its species were considered members of genus "Acacia" until 2009. "Vachellia" can be distinguished from other acacias by its capitate inflorescences and spinescent stipules. Before discovery of the New World, Europeans in the Mediterranean region were familiar with several species of "Vachellia", which they knew as sources of medicine, and had names for them that they inherited from the Greeks and Romans. The wide-ranging genus occurs in a variety of open, tropical to  subtropical habitats, and is locally dominant. In parts of Africa, "Vachellia" species are shaped progressively by grazing animals of increasing size and height, such as gazelle, gerenuk, and giraffe. The genus in Africa has thus developed thorns in defence against such herbivory. Nomenclature. By 2005, it had become clear that "Acacia sensu lato" needed to be split into at least five separate genera. The ICN dictated that under these circumstances, the name of "Acacia" should remain with the original type, which was "Acacia nilotica". However, that year the General Committee of the IBC decided that "Acacia" should be given a  new type ("Acacia verticillatum") so that the ~920 species of Australian acacias would not need to be renamed "Racosperma". This decision was opposed by 54.9% or 247 representatives at its 2005 congress, while 45.1% or 203 votes were cast in favor. However, since a 60% vote was required to override the committee, the decision was carried, and a "nom. cons. propositum" was listed in Appendix III (p. 286). The 2011 congress voted 373 to 172 to uphold the 2005 decision, which means that the name "Acacia" and a new type follow the majority of the species in "Acacia sensu lato , rather than this genus. However, some members of the botanical community remain dissatisfied. Description. The members of Vachellia" are trees or shrubs, sometimes climbing, and are always armed. Younger plants, especially, are armed with spines which are modified stipules, situated near the leaf bases. Some ("cf". "V. tortilis", "", "V. luederitzii" and "V. reficiens") are also armed with paired, recurved prickles (in addition to the spines). The leaves are alternate and bipinnately arranged, and their pinnae are usually opposite. The racemose inflorescences usually grow from the leaf axils. The yellow or creamy white flowers are produced in spherical heads, or seldom  in elongate spikes, which is the general rule in the related genus "Senegalia". The flowers are typically bisexual with numerous stamens, but unisexual flowers have been noted in "V. nilotica" ("cf". Sinha, 1971). The calyx and corolla are usually 4 to 5-lobed. Glands are usually present on the rachis and the upper side of the petiole. The seed pod may be straight, curved or curled, and either dehiscent or indehiscent. Species list. Of the 163 species currently assigned to "Vachellia", 52 are native to the Americas, 83 to Africa, Madagascar and the Mascarene Islands, 32 to Asia and 9  to Australia and the Pacific Islands. "Vachellia" comprises the following species: Section::::"Incertae sedis". These species are suspected to belong to "Vachellia", but have not been formally transferred.