Wikipedia
The term Uzazi refers to the dried fruit of the West African deciduous shrub Zanthoxylum tessmannii, syn. Fagara tessmannii, a member of the 'prickly ash' Zanthoxylum family. The name of the spice is derived from Igbo, a language in Nigeria, where the spice is grown and harvested on a commercial basis. Zanthoxylum tessmannii is a close relative of the Sichuan pepper, and Uzazi has a similar taste profile to the Asian spice. However, unlike Sichuan pepper where only the pericarp of the fruit is used, uzazi is used whole (both pericarp and seed). This may explain why uzazi has a spicier flavour and greater pungency than sichuan pepper. However, Cary Cairncross of Raw Decadence South Africa (http://www.spiceclub.co.za/) writes (personal communication): "I have an Igbo tribe supplier from Nigeria and he disagrees and says it is a local name for ashanti pepper (piper guineense)".
Even in West Africa this is a rare spice, and typically only five or six dried fruit are added to a dish.