The Collaborative International Dictionary of English v.0.48:

Flowering \Flow"er*ing\, a. (Bot.)
   Having conspicuous flowers; -- used as an epithet with many
   names of plants; as, flowering ash; flowering dogwood;
   flowering almond, etc.
   [1913 Webster]

   Flowering fern, a genus of showy ferns (Osmunda), with
      conspicuous bivalvular sporangia. They usually grow in wet
      places.

   Flowering plants, plants which have stamens and pistils,
      and produce true seeds; phenogamous plants; --
      distinguished from flowerless plants.

   Flowering rush, a European rushlike plant (Butomus
      umbellatus), with an umbel of rosy blossoms.
      [1913 Webster]

WordNet (r) 3.0 (2006):

flowering fern
    n 1: Australasian fern with clusters of sporangia on stems of
         fertile fronds [syn: flowering fern, Helminthostachys
         zeylanica]
    2: any fern of the genus Osmunda: large ferns with creeping
       rhizomes; naked sporangia are on modified fronds that
       resemble flower clusters [syn: flowering fern, osmund]