The Collaborative International Dictionary of English v.0.48:

Piperaceous \Pip`er*a"ceous\, a. [L. piper pepper.] (Bot.)
   Of or pertaining to the order of plants (Piperace[ae]) of
   which the pepper (Piper nigrum) is the type. There are
   about a dozen genera and a thousand species, mostly tropical
   plants with pungent and aromatic qualities.
   [1913 Webster] Piperazine