The Collaborative International Dictionary of English v.0.48:

Welwitschia \Wel*witsch"i*a\, n. [NL. So named after the
   discoverer, Dr. Friedrich Welwitsch.] (Bot.)
   An African plant (Welwitschia mirabilis) belonging to the
   order Gnetaceae. It consists of a short, woody, topshaped
   stem, and never more than two leaves, which are the
   cotyledons enormously developed, and at length split into
   diverging segments.
   [1913 Webster]

WordNet (r) 3.0 (2006):

welwitschia
    n 1: curious plant of arid regions of southwestern Africa having
         a yard-high and yard-wide trunk like a turnip with a deep
         taproot and two large persistent woody straplike leaves
         growing from the base; living relic of a flora long
         disappeared; some may be 700-5000 years old [syn:
         welwitschia, Welwitschia mirabilis]