Viburnum rhytidophyllum Hemsl. (China) – A rare but much increasing escape from cultivation. Its naturalization history in Belgium is rather poorly documented although it was already claimed as “naturalizing” in a road verge by a motorway in Wijnegem in 1990. From 2000 onwards Viburnum rhytidophyllum has been increasingly reported as an escape from cultivation. Most records are obviously bird-sown (seedlings and saplings under taller bushes and trees). Initially it was mainly confined to climatologically suitable areas, for instance in coastal dunes. In Oostduinkerke (Witte Burg), for instance, it was already firmly established in 2001 (Verloove 2002) and by now has further extended. Some of the older wild bushes flower and fruit profusely and a local naturalization seems very reasonable. Identical behaviour has been reported from several other localities in coastal dunes in recent years, for instance near De Haan, De Panne, Knokke, Oostduinkerke, etc. In the past years it was also increasingly recorded in inland localities, for instance from old walls, railway yards and railway tracks, waste land, deciduous woodland, coalmine heaps, etc. Also frequently seen (wild) in plantations. In Kortrijk (Kennedybos and nearby woody talus slope of E17-motorway) it occurs with several tens and looks perfectly naturalized. By now known from numerous, very widely localities (see waarnemingen.be for an overview at: http://waarnemingen.be/soort/view/156852) but almost absent from Wallonia. There known, for instance, on a coalmine heap near Charleroi (2011).
Similar behaviour recently became obvious in neighbouring territories as well. Viburnum rhytidophyllum now is a common evergreen invasive species in semi-natural woodlands in the German Ruhrgebiet (Fuchs & al. 2006). According to Walther (1999) it is a typical example of an evergreen species that is recently increasing as a result of climate change (laurophyllisation). Recently also reported as an escape from cultivation in the United States (see for instance Weckman & al. 2002). Future invasive behaviour, especially in climatologically suitable areas, seems very likely.
Some records might be referable to Viburnum xrhytidophylloides, its hybrid with V. lantana. This nothotaxon is more or less deciduous, has slightly wider and shorter leaves that are less wrinkled.
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