thallus

Term: thallus (pl thalli)

Origin: Anc Greek

θαλλός/thallos(=young shoot) > θρέφω/threpho(=feed)

Definition:

Thallus is the undifferentiated tissue of some algae, fungus, and other lower organisms  as liverworts and  lichens which are not  organized into distinct parts as leaves and roots.