Family: Fabaceae (Caesalpinoideae)
In English this tree is called gum or Zanzibar copal, or amber tree, and its local names are mnangu and mtandarusi. Formerly scientists knew it by the name Trachylobium verrucosum. Beware that the Byrsocarpus boivinianus tree is also called mnangu. Gum copal is found in dry coastal forest and tall damp miombo in southern Tanzania. It is native to the Indian Ocean rim, and is widely planted in botanic gardens in the tropics. The leaves of this tree are highly distinctive, being divided symmetrically into two leaflets although this is only evident close-up. However, it is not always easy to spot these leaflets as the tree is tall and seldom has low-hanging branches. Dependent on soil moisture levels, the tree sheds most of its leaves in the dry season. The trunk is smooth and grey, and frequently has a cleft or is hollow as a result of damage from tapping the resin. Slashing the bark reveals red coloured wood underneath. The flowers are pale, open and about 4cm across. They are followed by the species’ unique fruit. These are small and hard, dotted on the exterior with bubbles of resin that set when the fruit drops. They are reddish-green when ripe, but turn brown on the ground. Parts of the fruit case are usually visible under gum copal trees, the black seeds are quickly eaten by animals.
In the eighteenth and nineteenth century the yellow resin was an important product in world commerce. It was exported from Kilwa to Europe and the Arabian Peninsula where it was used to make varnish but these uses were superseded by synthetic chemicals. In recent years there has been a small resurgence in the use of gum copal in floor sealant. These days there is more demand for the tree’s timber.