Definition of: protonema

(prō′tə·nē′mə) noun plural ·ne·ma·ta (-nē′mə·tə) Bot.
An early stage in the development of the prothallium of ferns; a green confervoid or filamentous structure developed from the spore in mosses, on which the leafy plant arises as a lateral or terminal shoot. Also pro′to·neme (-nēm). [<NL <Gk. prōtos first + nēma a thread]