Thallus vs. Prothallus — What's the Difference?

Thallus (plural: thalli), from Latinized Greek θαλλός (thallos), meaning "a green shoot" or "twig", is the vegetative tissue of some organisms in diverse groups such as algae, fungi, some liverworts, lichens, and the Myxogastria. Many of these organisms were previously known as the thallophytes, a polyphyletic group of distantly related organisms.

A prothallus, or prothallium, (from Latin pro = forwards and Greek θαλλος (thallos) = twig) is usually the gametophyte stage in the life of a fern or other pteridophyte. Occasionally the term is also used to describe the young gametophyte of a liverwort or peat moss as well.

A plant body undifferentiated into stem, root, or leaf.

A small, flat, delicate structure produced by a germinating spore and bearing sex organs. It is the gametophyte of ferns and some other plants.

The main body of an alga, fungus, or lichen.

A prothallium.

(botany) An undifferentiated plant body, such as in algae.

The minute primary growth from the spore of ferns and other Pteridophyta, which bears the true sexual organs; the oöphoric generation of ferns, etc.

(botany) Any plant body lacking vascular tissue.

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.

A plant body without true stems or roots or leaves or vascular system; characteristic of the thallophytes