The Collaborative International Dictionary of English v.0.48:

Araceous \A*ra"ceous\, a. [L. arum a genus of plants, fr. Gr.
   ?.] (Bot.)
   Of or pertaining to an order of plants, of which the genus
   Arum is the type.
   [1913 Webster]

WordNet (r) 3.0 (2006):

araceous
    adj 1: relating to a plant of the family Araceae [syn: aroid,
           araceous]