so·rus 
(sôrəs)
(sôrəs)n. pl. so·ri (sôrī)
1. A cluster of sporangia borne on the underside of a fern frond. Also called fruit dot.
2. A reproductive structure in certain fungi and lichens.
[New Latin sōrus, from Greek sōros, heap; see teuə- in the Appendix of Indo-European roots.]
sorussori on the frond of
a polypody fern