What are those puffballs on this tree? They're anthers! In these acacias from the Tanzania-Kenya border, the showy part of the flower isn't the petal, but the anther - and with lots of anthers crowded together from many different flowers in a "head", they look more like a cheerleader's pom-pom than the butterfly-like pea flowers many of us are used to seeing. These capitate flowers are common in the Mimosoid clade of the pea family, Fabaceae, as are stipular spines and compound leaves.
Until about 20 years ago, these acacias were in the genus Acacia, but since then, they have been moved to Vachellia. This decision was (and remains) highly controversial, given the importance of acacias to African savannas and concerns about colonial attitudes in science. A lot of botanists continue to use acacia as a common name, but Vachellia as a scientific name.
