Definitions

1. noun

A spore produced by a fern or other pteridophyte in a two-layered sporangium.

“The botanist examined the fern’s mesospores under a microscope.”

2. noun

A spore produced by a fern or other pteridophyte in a two-layered sporangium, especially when referring to the spores of a fern genus (Marsilea).

“The mesospores of the Marsilea genus are of particular interest to fern researchers.”