soredium

from The Century Dictionary.

• noun In lichenology, a single algal cell or a group of algal cells wrapped in more or less hyphal tissue, which serves the purpose of vegetative propagation: commonly in the plural.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Bot.) A patch of granular bodies on the surface of the thallus of lichens.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun mycology A scalelike structure of algal cells in a lichen, enveloped in a network of hyphae and capable of independent vegetative growth.