Definition of prothallus in US English:

prothallus

noun

Botany
  • The gametophyte of ferns and other primitive plants.

    • ‘Here I re-examine the formation of the prothallus in a fern gametophyte in the context of a ‘whole-plant’ developmental response.’

Origin

Mid 19th century: modern Latin, from pro- ‘before, earlier’ + Greek thallos ‘green shoot’.

Pronunciation

prothallus

/prōˈTHaləs/