Cyperus longus L. (Old World) – An increasing alien of rather uncertain origin and status, formerly chiefly introduced as a casual alien with wool in the Vesdre valley (often rather distinct infraspecific taxa – see above). The taxon currently found in Belgium (chiefly in Flanders) mostly is a tall plant with many, long rays and broad leaves and belongs to C. longus s.str. (subsp. longus). At least part of the Belgian populations are probably relics of cultivation (or deliberately planted, even in semi-natural areas) or garden escapes (throw-outs). Some populations are found in more or less remote locations and could have been introduced by migrating birds, possibly from nearby, natural populations in neighbouring countries. Known since 2009 from the nature reserve Fluithoekduinen in Koksijde. Two clumps appeared in coastal dunes shortly after removal of the topsoil, along with several very rare and vulnerable native species (viz Carex punctata). It is not impossible that these species (incl. Cyperus longus) emerged from a very old exposed seedbank (and that the latter formerly was a rare native in Belgium, for instance in the Middle Ages). Cyperus longus is usually found in small numbers in ditches, pond margins or more rarely on dumps.
Worthwhile mentioning is the historical presence of a more slender taxon [subsp. badius (Desf.) Murb.; syn.: C. badius Desf.] at the thermal springs of Spa, at least since 1816 but long gone by now (see also Savelsbergh 1997 and Desfayes 2004 for identical records in nearby Germany and elsewhere in Europe). It is sometimes given specific rank but obviously very closely related to Cyperus longus (see however Desfayes 2004).
Selected literature
Collins R.P., McNally S.F., Simpson D.A. & Jones M.B. (1988) Studies on infraspecific variation in Cyperus longus L. from Europe. New Phytol. 110(2): 279-289.
Desfayes M. (2004) The specific status of Cyperus badius and the subspecies of Scirpoides holoschoenus (Cyperaceae), with special reference to Sardinia. Fl. Medit. 14: 173-188.
Henrion E. (2007) Deux espèces de Cyperus découvertes simultanément. Adoxa 57: 7-8.
Savelsbergh E. (1997) Cyperus longus ssp. badius (Desf.) Murb. im letzten Jahrhundert am 'Warmen Bach' und an 'Warmen Weiher' zu Burtscheid sudlich Aachen (TK 25 5202/23). Decheniana 150: 43-49.
Verloove F. (2002) Ingeburgerde plantensoorten in Vlaanderen. Mededeling van het Instituut voor Natuurbehoud n° 20: 227 p.