Why is the rate of hybridization so high in Blue Hills Polypodys?
It is well over 90%.
At Mt. Wachusett it seems to be more like 1%, if that. All P. appalachianum, though in the Blue Hills that is the third-most poplulous taxon of the three. (diploid P. appalachianum, tetraploid P. virginianum, and their triploid hybrid)
I guess one project would be to try to actually measure those ratios at a number of sites. Nowhere I have seen is the hybrid so abundant as in the Blue Hills. It seems to dissappear gradually as one goes westward.
Another project would be to determine genetic identity beyond all doubt by squashing growing cells and staining them enough to count the chromosomes.
And then the challenge would be to discover what unorthodox reproduction technique the Blue Hills Polypody hybrids are using. The literature mentions unreduced mother cells in another Polypody hybrid. I think I have seen them, occasionally: slightly larger yellow spheres among the aborted pale reniform spores the hybrid tries to produce. But there aren't very many of them.
In the image, the hybrid is between its parents, P. appalachianum on the left, P. virginianum on the right.
