The Collaborative International Dictionary of English v.0.48:
Petalous \Pet"al*ous\, a. Having petals; petaled; -- opposed to apetalous. [1913 Webster]WordNet (r) 3.0 (2006):
petalous adj 1: (of flowers) having petals [syn: petalous, petaled, petalled] [ant: apetalous, petalless]