Polystichum tsus-simense J. Smith (syn.: P. mayebarae Tagawa) (SE-As.) – An exceptional garden escape, discovered on an old wall of a private garden in the city of Gent in 2006 and on a basement wall in the city of Antwerp in 2016 (confirmed subsequently). In 2017 also found in riparian woodland in Lanaken (Hochter Bampd). The species is not very frost-sensitive and thus likely to persist, although only single individuals have been recorded so far. Also recorded as a greenhouse weed, for instance in the Botanic Garden of Meise.
Crouch H.J. & Rumsey F. (2009) Changes in the fern flora of the city of Bath. Somerset Archaeology and Natural History 153: 233-246. [available online at: http://www.sanhs.org/Documents/153/CrouchRumsey.pdf]
Robinson R. (2006) Fern hunting in NW1. Newsletter of the London Natural History Society 195: 5.
Verloove F., van der Ham R. & Denters T. (2007) Exotische muurvarens in België en Nederland. Dumortiera 92: 1-16.