thallogen

Thal"lo*gen, n. Etym: [Gr. -gen.] (Bot.) Defn: One of a large class or division of the vegetable kingdom, which includes those flowerless plants, such as fungi, algæ, and lichens, that consist of a thallus only, composed of cellular tissue, or of a congeries of cells, or even of separate cells, and never show a distinction into root, stem, and leaf.

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