FERN SPORES

Fern spores are microscopic haploid reproductive cells that develop into the gametophyte generation of a fern. The spores are encapsulated in sacs called sporangia, which aggregate into sori in genus-specific patterns, usually on the undersurface of the fern fronds.  Spores from homosporous ferns range in size from 20 – 100 microns. Brian Aiken, curator of the American Fern Society spore exchange, estimates that 99% of the spores that are in the AFS exchange will pass through a 76-micron sieve. Within genera there is a lot of variability. Here are 6 examples from Tyron’s Spores of the Pteridophyta (1): Dryopteris 20-70 microns, Thelypteris 27-57, Polypodium 33-80, Pyrrosia 42-110, Asplenium 23-60, and Lygodium 53-127

Spores are ejected after the sori mature, and the timing of this maturation varies with fern genera and species.  Because they are microscopic, they can be carried for long distances by winds and develop into mature sporophyte ferns when the right environmental conditions are present.  Because ferns have survived at least four mass extinction events, they are potentially valuable species to study during climate changes.  

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(1) Alice F. F. Tryon, Bernard Lugardon (1991) Spores of the Pteridophyta (1st Edition)