Sori of the Oak Fern, Gymnocarpium dryopteris, are produced on the back of the leaflets. Each sorus, composed of 50 or so sporangia, appears to the naked eye like a little brown dot on the back of the leaflet. Gymnocarpium sori lack an indusium. Right click to Download hi-res photo file. File size:338kb Type:JPG
Spores of the Oak Fern. These spores are about 40 microns long. Less than half the thickness of a hair.