Usually, Sichuan pepper is not considered a true pepper. Which means that it isn't regarded botanically to belong to the traditional families of plants that have a sharp taste and parts therof are employed as a peppery ingredient in dishes. That observation also means that a number of families within the flora must exist that can indeed be seen as peppers. That's right.
Broadly speaking these families are diveded into [1] the 'real' peppers, genus Piperita from the pepper family (Piperaceae), [2] the chilli peppers, the genus Capsicum from the nightshade family (Solanaceae), and [3] the pimentas, the genus Pimenta from the myrtle family (Myrtaceae).
Not everyone was forunate enough to like in an area where one of these families of peppers was growing abundantly, but humans have always had an unconscious tendency to spice its food. So they went diligently in search of alternatives. Sichuan pepper got its name from the Chinese province of Sichuan en consists of the dried husk from a small fruit from one of several species of the genus Zanthoxylum. In the majority of cases it will turn out to be Zanthoxylum piperitum and to a lesser extent Zanthoxylum simulans and Zanthoxylum