Juncus xiphioides E. Mey. (SW USA, NW Mexico) – An exceptional alien. A relatively large, seemingly well-established population was discovered on damp sand in Blankenberge in 2016 (see Verloove & al., in prep.). The plants were found on the grounds of the abandoned sand sculpture festival but the vector of introduction remains obscure. Contrary to the related and similar Juncus ensifolius, this species is only rarely grown as an ornamental. There seem to be no other records of this species outside of the New World.
Juncus xiphioides is in all parts more robust than J. ensifolius: its leaves are wider (up to 16 mm wide in Blankenberge) and its culms taller (usually more than 60 cm tall, in Blankenberge up to 120 cm tall). Its flowers have six stamens, not three like in J. ensifolius var. ensifolius. Compared with the latter its flower heads are relatively few-flowered and fairly lax (12-20 flowers per head, much less frequently congested and with up to 70 flowers) and much paler in color, usually reddish brown. Moreover, inflorescences are paniculate with more numerous flower heads that are very widely spaced.
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Selected literature:
Brooks R.E. & Clemants S.E. (2000) – Juncus. In: Flora of North America Editorial Committee (eds.), Flora of North America, vol. 22. Oxford University Press, New York-Oxford: 211-255.
Kirschner J. (2002a) – Species Plantarum. Flora of the world. Juncus subg. Juncus. Vol. 7(2). Australian Biological Resources Study, Canberra: VIII + 336 p.
Kirschner J. (2002b) – Species Plantarum. Flora of the world. Juncus subg. Agathryon. Vol. 8(3). Australian Biological Resources Study, Canberra: VIII + 192 p.
Verloove F., Van Vooren P. & Mortier B. (in press) Juncus section Iridifolii (Juncaceae) in Belgium. Dumortiera.