The Collaborative International Dictionary of English v.0.48:

Flower-fence \Flow"er-fence`\, n. (Bot.)
   A tropical leguminous bush (Poinciana pulcherrima, or
   C[ae]salpinia, pulcherrima) with prickly branches, and
   showy yellow or red flowers; -- so named from its having been
   sometimes used for hedges in the West Indies. --Baird.
   [1913 Webster]