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.

Source: Webster's Revised Unabridged Dictionary (1913)
 

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: Webster's Revised Unabridged Dictionary (1913)