The Collaborative International Dictionary of English v.0.48:

slipper orchid \slipper orchid\ n.
   any of several chiefly American wildflowers having an
   inflated pouchlike lip; difficult or impossible to cultivate
   in the garden.

   Syn: lady's slipper, lady's-slipper, lady-slipper.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

slipper orchid
    n 1: any of several chiefly American wildflowers having an
         inflated pouchlike lip; difficult or impossible to
         cultivate in the garden [syn: lady's slipper, lady-
         slipper, ladies' slipper, slipper orchid]