So·rus n.; pl. Sori
1. Bot. One of the fruit dots, or small clusters of sporangia, on the back of the fronds of ferns.
2. (a) In parasitic fungi, any mass of spores bursting through the epidermis of a host plant. (b) In lichens, a heap of soredia on the thallus.
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sorus
n 1: a spore-producing structure in certain lichens and fungi
2: cluster of sporangia usually on underside of a fern frond
[also: sori (pl)]