Source : Webster's Revised Unabridged Dictionary (1913)

Apetalous \A*pet"al*ous\ ([.a]*p[e^]t"al*[u^]s), a. [Pref. a-
   not + petal.] (Bot.)
   Having no petals, or flower leaves. [See Illust. under
   {Anther}].

Source : WordNet®

apetalous
     adj : of flowers; having no petals [syn: {petalless}] [ant: {petalous}]