Thal·lus n.; pl. Thalli Bot. A solid mass of cellular tissue, consisting of one or more layers, usually in the form of a flat stratum or expansion, but sometimes erect or pendulous, and elongated and branching, and forming the substance of the thallogens.
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thallus
n : a plant body without true stems or roots or leaves or
vascular system; characteristic of the thallophytes
[also: thalli (pl)]