an organism not differentiated into shoot and root, the cells of which have a cell wall; originally used for bacteria, fungi and algae.

The thallophytes are a polyphyletic group of non-mobile organisms traditionally described as "relatively simple plants" or "lower plants" with undifferentiated bodies (thalli). They were a defunct division of Kingdom Plantae, the Thallophyta (or Thallobionta) that included fungus and algae, and lichens occasionally bacteria and the Myxomycophyta.