Polystichum polyblepharum (Roemer ex Kunze) C. Presl (SE As.) – A very rare but possibly overlooked escape from cultivation. Known since 2014 from at least three localities. First discovered in Boom on an old brick wall, along with P. aculeatum and P. setiferum. Furthermore known from woodland in Dessel and Tiegem (in the latter locality also with P. setiferum).
This species is widely cultivated now as an ornamental and seems to escape fairly easily. Similar records are known, for instance, from the Netherlands and the British Isles (e.g. http://waarneming.nl/soort/view/187452, Edgington 2010).
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Selected literature:
Daigobo S. (1972) Paper chromatographical studies on the hybrids and their putative parents in Japanese Polystichum polyblepharum group (in Japanese). J. Jap. Bot. 47(9): 261-268.
Edgington J. (2010) The fern flora of inner London. London Naturalist 89: 19-29.
Kurata S. (1979) Additional notes on the Japanese ferns belonging to the Polystichum polyblepharum group: 1. (in Japanese). J. Nipp. Fern Club 2 (suppl. 1): 336-340.
Kurata S. (1979) On the Japanese ferns belonging to the Polystichum polyblepharum group. J. Nipp. Fern Club 2 (suppl. 1): 307-335.
Serizawa S. (1979) New species and hybrids of the Japanese Polystichum polyblepharum group. J. Jap. Bot. 54(5): 137-145.