Source : Webster's Revised Unabridged Dictionary (1913)

Alga \Al"ga\, n.; pl. {Alg[ae]}. [L., seaweed.] (Bot.)
   A kind of seaweed; pl. the class of cellular cryptogamic
   plants which includes the black, red, and green seaweeds, as
   kelp, dulse, sea lettuce, also marine and fresh water
   conferv[ae], etc.

Cryptogamia \Cryp`to*ga"mi*a\ (kr?p`t?-g?"m?-?), n.; pl.
   {Cryptogami[ae]} (-?). [NL., fr. Gr. krypto`s hidden, secret
   + ga`mos marriage.] (Bot.)
   The series or division of flowerless plants, or those never
   having true stamens and pistils, but propagated by spores of
   various kinds.

   Note: The subdivisions have been variously arranged. The
         following arrangement recognizes four classes: -- I.
         {{Pteridophyta}, or {Vascular Acrogens}.} These include
         Ferns, {Equiseta} or Scouring rushes, {Lycopodiace[ae]}
         or Club mosses, {Selaginelle[ae]}, and several other
         smaller orders. Here belonged also the extinct coal
         plants called {Lepidodendron}, {Sigillaria}, and
         {Calamites}. II. {{Bryophita}, or {Cellular Acrogens}}.
         These include {Musci}, or Mosses, {Hepatic[ae]}, or
         Scale mosses and Liverworts, and possibly
         {Charace[ae]}, the Stoneworts. III. {{Alg[ae]}}, which
         are divided into {Floride[ae]}, the Red Seaweeds, and
         the orders {Dictyote[ae]}, {O["o]spore[ae]},
         {Zo["o]spore[ae]}, {Conjugat[ae]}, {Diatomace[ae]}, and
         {Cryptophyce[ae]}. IV. {{Fungi}}. The molds, mildews,
         mushrooms, puffballs, etc., which are variously grouped
         into several subclasses and many orders. The {Lichenes}
         or Lichens are now considered to be of a mixed nature,
         each plant partly a Fungus and partly an Alga.

Source : WordNet®

algae
     n : primitive chlorophyll-containing mainly aquatic eukaryotic
         organisms lacking true stems and roots and leaves [syn: {alga}]