1. Persicaria capitata (Buch.-Hamilt. ex D. Don) H. Gross (syn.: Polygonum capitatum Buch.-Hamilt. ex D. Don) (SE-As.) – A very rare but recently increasing garden escape, known since 2001. Usually ephemeral or sometimes persisting for some time but probably not really becoming naturalized (yet). In Gent (railway station Sint-Pieters) recorded during several years (Van Landuyt & Molenaar 2002, Verloove 2002) but now gone. Furthermore regularly reported from several different (larger) cities, especially in Flanders. Persicaria capitata is frequently grown for ornament nowadays (especially to decorate hanging baskets). It easily self-seeds and locally germs in urban areas: foot of walls, pavement,… usually in sun-exposed, dry places.
Persicaria capitata is surprisingly more frequent and more or less naturalised in urban areas in the Netherlands (Denters 2004) and, to some extent, in the British Isles as well although it possibly is not fully hardy (Stace 2010). In several parts of the world Persicaria capitata is increasingly reported as an invasive environmental weed (see for instance Meier 2006).
A rather similar species, Persicaria runcinata (Buch.-Hamilt. ex D. Don) H. Gross (syn.: Polygonum runcinatum Buch.-Hamilt. ex D. Don), was recently found as an escape in the British Isles (Macpherson & Clement 2003). It also is a perennial with capitate inflorescences but it has erect stems and leaves like in Persicaria nepalensis (with a distinctly winged petiole).
Selected literature:
Clement E.J. (1983) Some rare Polygonaceae. BSBI News 34: 29-30.
Denters T. (2004) Stadsplanten. Veldgids voor de stad. Fontaine Uitgevers, ‘s-Graveland: 432 p.
Macpherson P. & Clement E.J. (2003) Persicaria runcinata in the Clyde Valley (V.C. 77). BSBI News 92: 44-45.
Meier W. (2006) Contribución al conocimiento de Persicaria nepalensis (Meisn.) H. Gross y P. capitata (Buch.-Ham. ex D. Don) H. Gross, especies invasoras en el Parque Nacional El Avila, Venezuela. Acta Bot. Venez. 29(1): 1-16.
Stace C. (2010) New flora of the British Isles, 3th ed.: XXXII + 1232 p. Cambridge University Press.
Van Landuyt W. & Molenaar E. (2002) Polygonum capitatum, een verwilderde bodembedekker in Gent en Antwerpen. Dumortiera 79: 19-21.
Verloove F. (2002) Ingeburgerde plantensoorten in Vlaanderen. Mededeling van het Instituut voor Natuurbehoud n° 20: 227 p.