The Collaborative International Dictionary of English v.0.48:

Apocynaceous \A*poc`y*na"ceous\, Apocyneous \Ap`o*cyn"e*ous\, a.
   [Gr. ? dogbane; ? from + ? dog.] (Bot.)
   Belonging to, or resembling, a family of plants, of which the
   dogbane (Apocynum) is the type.
   [1913 Webster]

WordNet (r) 3.0 (2006):

apocynaceous
    adj 1: of or relating to tropical plants of the family
           Apocynaceae