Ruscus aculeatus L. (Medit., SW-Eur., Macaronesia) – A very rare escape from or, more likely, relic of cultivation. Already known in Belgium in the 18th century (e.g. Durand 1899). Its residence status and degree of naturalization in Belgium are contested. Ruscus aculeatus is native in northern France, close to the Belgian frontiers, and is sometimes claimed to be native in Belgium as well (see for instance Yeo 1986). The species is usually found in deciduous woodland, often in more or less (semi-) natural habitats. However, at least part of the populations are mere relics of cultivation (plants are highly resistant to unfavorable conditions and neglect; see Yeo l.c.). As such, Ruscus aculeatus can persist for several decades (e.g. Olne, Jalhay, etc.) but it has probably disappeared from most of its historical locations by now (except perhaps in Olne where it was still present in 2012). Probably the largest extant population is located on the margins of a pine wood in the nature reserve Bourgoyen-Ossemeersen near Gent where it is known at least since 1990. It is also known from old estates in Kortrijk (Paters Mote), Loppem, Edegem (Hof ter Linden), etc. A single individual also survives in scrub in coastal dunes in De Panne (on the verge of the Houtsaegherduinen nature reserve). An overview of Belgian records is available here: http://waarnemingen.be/soort/view/121609.
A recent, extensive account of Ruscus aculeatus in the British Isles, with numerous additional references, is provided by Thomas & Mukassabi (2014).
Selected literature:
Bolman J. (1973) Muizendoorn (Ruscus aculeatus L.) een plant met bessen op de bladeren. Natura (Amsterdam) 70: 37-41.
Cann D.C.G. (2001) Ruscus aculeatus 'Lanceolatus'. The New Plantsman 8(4): 239-243.
Durand Th. (1899) Prodrome de la flore belge. Tome III Phanérogames. Editions A. Castaigne, Bruxelles: 1112 p.
Fitter R. (1992) When does Butcher's-Broom start to flower? B.S.B.I. News 62: 12-13. [available online at: http://archive.bsbi.org.uk/BSBINews62.pdf]
Hillman E.M. (1979) A study of Ruscus aculeatus on Bookham Common. London Naturalist 58: 44-55.
Hillman E.M. & Warren A.A. (1973) A survey of Ruscus aculeatus on Bookham Common. London Naturalist 52: 96-103.
Hirsch A.M. (1977) A developmental study of the phylloclades of Ruscus aculeatus L. Bot. J. Linn. Soc. 74(4): 355-365.
Kay Q.O.N. & Page J. (1985) Dioecism and pollination in Ruscus aculeatus. Watsonia 15: 261-264.
Lawrence E. (1963) Butcher’s Broom - Ruscus aculeatus. American Horticulture Magazine 42(2): 125-126.
Robert P. (1964) Contribution à l'étude ontogénique de Ruscus aculeatus L. Ann. Sci. Nat. Bot. Biol. Vég. 5 : 739-752.
Tauber F. (1975) Date corologice şi cenologice despre ghimpele (Ruscus aculeatus L. in Banat. Tibiscus 1975: 3-18.
Thomas P.A. & Mukassabi T.A. (2014) Biological Flora of the British Isles: Ruscus aculeatus. Journal of Ecology 102: 1083-1100. [available online at: http://onlinelibrary.wiley.com/doi/10.1111/1365-2745.12265/epdf]
Walls R. (1992) Butcher's Broom (Ruscus aculeatus L.). Recording Dorset 2: 21.
Yeo P.F. (1986) Ruscus. In: Walters S.M. & al. (eds.), The European Garden Flora, vol. 1: 265-266. Cambridge University Press, Cambridge.