from
The Collaborative International Dictionary of English v.0.48
Monopetalous \Mon`o*pet"al*ous\, a. [Mono- + petal: cf. F.
monop['e]tale.] (Bot.)
Having only one petal, or the corolla in one piece, or
composed of petals cohering so as to form a tube or bowl;
gamopetalous.
[1913 Webster]
Note: The most recent authors restrict this form to flowers
having a solitary petal, as in species of {Amorpha},
and use {gamopetalous} for a corolla of several petals
combined into one piece. See Illust. of {Gamopetalous}.
[1913 Webster]