[6] In Ireland, it is rare and concentrated in the east of the country, leading Praeger to conjecture that the Irish examples are recent colonists from Great Britain, arriving as airborne spores.

[7] It is a rare, amber-listed plant of moderate conservation concern in the Isle of Man where it is a protected species listed on Schedule 7 of the Wildlife Act 1990.

[8][9] Similar plants, which may belong to the same species occur in East Asia and North America,[5] although these are usually considered a separate taxon.

[10] Spores attributable to C. crispa have been discovered in deposits in Snowdonia from the last glacial period, as well as from more low-lying sites in Cheshire.

[7] The parsley fern appeared in Carl Linnaeus' 1753 work Species Plantarum, the starting point for botanical nomenclature, under the name Osmunda crispa.