The Collaborative International Dictionary of English v.0.48:

Valonia \Va*lo"ni*a\, n. [It. vallonia, vallonea, fr. NGr.
   balania`, balanidia`, the holm oak, bala`ni, balani`di, an
   acorn, Gr. ba`lanos.]
   [1913 Webster]
   1. The acorn cup of two kinds of oak (Quercus macrolepis,
      and Quercus vallonea) found in Eastern Europe. It
      contains an abundance of tannin, and is much used by
      tanners and dyers.
      [1913 Webster]

   2. [Perhaps named from its resemblance to an acorn.] (Bot.) A
      genus of marine green algae, in which the whole frond
      consists of a single oval or cylindrical cell, often an
      inch in length.
      [1913 Webster]