The Collaborative International Dictionary of English v.0.48:

Sympetalous \Sym*pet"al*ous\, a. [Pref. sym- + petal.] (Bot.)
   Having the petals united; gamopetalous.
   [1913 Webster]

WordNet (r) 3.0 (2006):

sympetalous
    adj 1: having a corolla composed of partially or wholly fused
           petals forming a corolla shaped like a tube or funnel
           [syn: gamopetalous, sympetalous]