About Asplenium onopteris L.
Asplenium onopteris L. is difficult to distinguish from the related fern Asplenium adiantum-nigrum. The key biological difference between the two species is that A. onopteris is diploid, and it is one of the two parent species of the tetraploid A. adiantum-nigrum; the other parent is the diploid A. cuneifolium. When examined with a microscope, the most consistently observable difference between the two species is spore size. A. onopteris spores have a mean diameter of 28 μm, and almost all are smaller than 31 μm. In comparison, A. adiantum-nigrum spores have a mean diameter of 34 μm, and almost all are larger than 31 μm. The leaflets of a typical A. onopteris are narrower relative to their length than the leaflets of a typical A. adiantum-nigrum, but this trait is not a reliable method for identifying A. onopteris. Asplenium onopteris grows in western and central Europe, the Mediterranean Basin (including North Africa), and Macaronesia, excluding Cape Verde. Isolated populations have been recorded as far north as Ireland and Poland.
