\Va*lo"ni*a\, n. [It. vallonia, vallonea, fr. NGr.
balania`, balanidia`, the holm oak, bala`ni, balani`di, an
acorn, Gr. ba`lanos.]
1. The acorn cup of two kinds of oak ({Quercus macrolepis},
   and {Q. vallonea}) found in Eastern Europe. It contains
   abundance of tannin, and is much used by tanners and
   dyers.
2. [Perhaps named from its resemblance to an acorn.] (Bot.) A
   genus of marine green alg[ae], in which the whole frond
   consists of a single oval or cylindrical cell, often an
   inch in length.