Anemone xhybrida Paxton (A. hupehensis (Lemoine) Lemoine var. japonica (Thunb.) Bowles & Stearn x A. vitifolia Buch.-Ham. ex DC.) (Hort.) – A rare but increasing escape from or relic of cultivation. Although very commonly planted as an ornamental, Anemone xhybrida was not recorded prior to 2004 in Belgium (Verloove 2006) when it was seen self-sown in urban habitats in Gent. Since then it has been recorded in rather numerous and widely scattered other localities. In most, however, it is seen in small number. In some places it survives for years but a genuine naturalization process has not been observed so far.
Anemone xhybrida is usually seen on rough ground (where it may be associated with former gardens) and self-sown in urban environments (often foot of walls, cracks in pavement, etc.). It is also regularly seen on brick river walls, for instance in Brugge, Gent and Kortrijk. An overview of recent observations in Belgium is available here: https://waarnemingen.be/soort/view/150995.
It is uncertain whether or not the putative parental species of Anemone xhybrida are still cultivated these days in Belgium. According to most authors (e.g. Uotila 2001, Brickell 2011, Stace & al. 2015) this hybrid produced no achenes while at least some of the Belgian records clearly refer to plants that are self-sown. In Norden, A. hupehensis and A. tomentosa (Maxim.) C. P’ei have also been observed (Uotila l.c.). Thus, the identity of at least some plants now found in the wild in Belgium probably should be re-assessed. Plants with lobed but undivided basal leaves may point at A. vitifolia, while plants with densely tomentose lower leaf surfaces may belong to A. tomentosa. A. hupehensis probably most closely resembles A. xhybrida but it is a smaller plant (rarely exceeding 60 cm vs. often 120-150 cm), with less numerous, almost circular perianth segments (5-6 vs. 6-11 narrower segments) and it is fully fertile. Useful keys and additional details are presented by Kaiser (1995a) and McKendrick & al. (1998).
Selected literature
Bowles E.A. & Stearn W.T. (1947) The history of Anemone japonica. Journ. Roy. Hort. Soc. 72: 261-268 and 297-308.
Brickell C.D. (2011) Anemone and Pulsatilla. In: Cullen J. & al. (eds.), The European Garden Flora, vol. 2 (2nd ed.). Cambridge University Press: 367-375.
Hensen K.J.W. (1968) De in Nederland gekweekte Japanse anemonen. Beplantingen en Boomkwekerij 24: 127-134. [available online at: http://edepot.wur.nl/295445]
Hensen K.J.W. (1979) Voortgezet onderzoek van het sortiment Japanse Anemonen. Groen 9: 363-370.
Hop M.E.C.M. (2001) Herfstbloeiende Anemone. Dendroflora 38: 13-37. [available online at: https://core.ac.uk/download/pdf/29301220.pdf]
Kaiser K. (1995a) Herbstanemonen indentifizieren und benennen. Gartenpraxis 10: 22-24.
Kaiser K. (1995b) Herbstanemonen in der Gartenkultur. Gartenpraxis 11: 8-14.
McKendrick M. (1998) Japanese Anemones. The Garden 123(9): 628-633.
McKendrick M., Miller D. & Jones L. (1998) Japanese Anemone. Descriptions and key of Japanese Anemone grown in the Royal Horticultural Society's Trial 1995-1997, Royal Horticultural Society. [available online at: http://apps.rhs.org.uk/planttrials/TrialReports/Japanese%20Anemone%20199...
McKendrick M. (1990) Autumn Flowering Anemones. The Plantsman 12: 140-151.
Rudy M.R. (2004) Fall-blooming Anemones. Chicago Botanic Garden 25: 1-4. [available online at: https://www.chicagobotanic.org/downloads/planteval_notes/no25_anemones.pdf]
Stace C., Preston C.D. & Pearman D.A. (2015) Hybrid Flora of the British Isles. B.S.B.I., London: 501 p.
Uotila P. (2001) Anemone. In: Jonsell B. (ed.), Flora Nordica, vol. 2. The Bergius Foundation, Stockholm: 300-305.
Verloove F. (2006) Catalogue of neophytes in Belgium (1800-2005). Scripta Botanica Belgica 39: 89 p. [available online at: http://alienplantsbelgium.be/sites/alienplantsbelgium.be/files/tabel_2.pdf]