so·re·di·um (sə-rē'dē-əm) n.
pl.so·re·di·a (-dē-ə) A specialized asexual reproductive unit of lichens consisting of a mass of algal cells surrounded by fungal hyphae.
[New Latin sōrēdium, diminutive of Greek sōros, heap; see sorus.] so·re'di·al (-dē-əl) adj.