A vocabulary of landscape — a landscape of words
1190 entries
thallus
A thallus is a plant or plant-like body that is not divided into root, stem, and leaf. Seaweeds have one, so do lichens, liverworts, and many fungi. It is a body plan rather than a family. What the word marks is the absence of the specialized organs and internal plumbing that vascular plants have, so a kelp forty feet long and a lichen crust on a wall are described with the same term.
Etymology
The word is Greek for a young shoot or a green twig. Botany used to divide plants into the thallophytes, with no organs, and the cormophytes, with them, and although that classification has long been abandoned the word for the body survived because there is still no other single term for what a seaweed has.