a minute, flat, greenish disc of cells bearing sex organs on its lower side, usually attached to the ground by single-celled hairs, and forming the haploid, sexual generation of ferns and similar plants
: also proˈthallus (proʊˈθæliəs)Word forms: pluralproˈthalˌli (proʊˈθæliˌaɪ) or proˈthalluses
Derived forms
prothallial (proˈthallial) (proʊˈθæliiəl)
adjective or proˈthalˌloid (proʊˈθælˌɔɪd)
Word origin
ModL < Gr pro-, before + thallos, a shoot (< IE base *dhal-, to bloom > Alb dal, to sprout) + -ium