ringent

from The Collaborative International Dictionary of English v.0.48

Ringent \Rin"gent\, a. [L. ringens, -entis, p. pr. of ringi to
   open wide the mouth: cf. F. ringent.] (Bot.)
   Having the lips widely separated and gaping like an open
   mouth; as a ringent bilabiate corolla.
   [1913 Webster]