Australian species instead of the original African type species, an exception to traditional rules of priority that required ratification by the International Botanical Congress. That decision has been controversial, and debate continued, with some taxonomists (and many other biologists) deciding to continue to use the traditional Acacia sensu lato circumscription of the genus, in defiance of decisions by an International Botanical Congress. However, a second International Botanical Congress has now confirmed the decision to apply the name Acacia to the mostly Australian plants, which some had been calling Racosperma, and which had formed the overwhelming majority of Acacia sensu lato. Debate continues regarding the traditional acacias of Africa, possibly placed in Senegalia and Vachellia, and some of the American species, possibly placed in Acaciella and Mariosousa. Acacias belong to the subfamily Mimosoideae, the major clades of which may have formed in response to drying trends and fire regimes that accompanied increased seasonality during the late Oligocene to early Miocene (~25 mya). Pedley (1978), following Vassal (1972), viewed Acacia as comprising three large subgenera, but subsequently (1986) raised the rank of these groups to genera Acacia, Senegalia (s.l.) and Racosperma, which was underpinned by later genetic studies. In common parlance, the term "acacia" is occasionally applied to species of the genus Robinia, which also belongs in the pea family. Robinia pseudoacacia, an American species locally known as black locust, is sometimes called "false acacia" in cultivation in the United Kingdom and throughout Europe. Description The leaves of acacias are compound pinnate in general. In some species, however, more especially in the Australian and Pacific Islands species, the leaflets are suppressed, and the leaf-stalks (petioles) become vertically flattened in order to serve the purpose of leaves. These are known as "phyllodes". The vertical orientation of the phyllodes protects them from intense sunlight since with their edges towards the sky and earth they do not intercept light as fully as horizontally placed leaves. A few species (such as Acacia glaucoptera) lack leaves or phyllodes altogether but instead possess cladodes, modified leaf-like photosynthetic stems functioning as leaves. The small flowers have five very small petals, almost hidden by the long stamens, and are arranged in dense, globular or cylindrical clusters; they are yellow or cream-colored in most species, whitish in some, or even purple (Acacia purpureopetala) or red (Acacia leprosa 'Scarlet Blaze'). Acacia flowers can be distinguished from those of a large related genus,