The Collaborative International Dictionary of English v.0.48:

Monophyllous \Mo*noph"yl*lous\, a. [Gr. mono`fyllos; mo`nos
   alone + fy`llon leaf: cf. F. monophylle.] (Bot.)
   One-leaved; composed of a single leaf; as, a monophyllous
   involucre or calyx.
   [1913 Webster]