soredium A microscopic structure formed by certain lichens as a means of vegetative propagation: it consists of a few fungal hyphae among which are enmeshed a few cells of the phycobiont. To the naked eye, soredia in masses appear as a granular or fine powder.

soredium (pl. soredia) A small body, consisting of a core of algal cells surrounded by fungal hyphae, that functions as a structure of vegetative propagation in lichens. Soredia, which range from 25 to 100 μm in diameter, are released like spores and are dispersed in air currents. Compare isidium.