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(1) The green or blue-green algae that, together with fungi, form the lichens. Previously the gonidia were incorrectly considered the reproductive organs of lichens.
(2) In filamentous bacteria, the motile or nonmotile cells that separate from the filament and serve for reproduction.
(3) The small globular nonmotile cells that serve for reproduction in some blue-green algae (order Chamaesiphonales), and also the cells into which the body of the algae sometimes breaks up during reproduction.
(4) An obsolete name for the spores of algae and fungi, formed by asexual means and serving for reproduction.