photobiont (noun, pl. photobionts;ecology term) – the photosynthetic partner of a lichen symbiosis, i. e., a population of photosynthetic organisms that inhabit a lichen thallus, either a population of prokaryotic (cyanobacteria, cf. cyanobiont) or eukaryotic algae (mostly green algae, cf. chlorobiont). Related terms: alga, primary photobiont, secondary photobiont.