Juncus

Juncus is a large, nearly cosmopolitan genus of ca. 310 species (Mabberley 2008). About 20 species are native in Belgium as well (see Lambinon & al. 2004 for an extensive overview), although some are exceedingly rare or extinct now. Most species are very unshowy and have no or little ornamental value. As a result, Juncus is not very popular in cultivation. In fact, most species in cultivation are native in Belgium as well. Some (mainly American) species are more or less weedy in natural habitats, especially in heaths.

1. Leaves and stems conspicuously flattened, Iris-like === 2

1. Leaves and stems terete or slightly flattened, never Iris-like === 3

2. Widest leaves more than 10 mm wide. Plant robust, usually more than 60 cm tall. Stamens six === Juncus xiphioides

2. Leaves at most 6 mm wide. Plant slender and much smaller. Stamens three === J. ensifolius (var. ensifolius)

3. Inflorescence appearing lateral (inflorescence bract erect, as a continuation of the culm). Plant always perennial (native) === Juncus arcticus, J. conglomeratus, J. effusus, J. filiformis, J. inflexus and J. maritimus

3. Inflorescence appearing terminal. Plant annual or perennial === 4

4. Flowers borne singly or in groups of 2-3(-5), each flower subtended by two bracteoles === 5

4. Flowers borne in groups of (2-) 3-50, bracteoles absent (but heads often subtended by small bracts) === 9

5. Annual, plant easily uprooted. Usually rather small plants, rarely exceeding 30 cm  === 6

5. Perennial. Usually taller plants, often more than 30 cm === 8

6. Capsule subglobular. Flowers always solitary. Lower leaf sheaths auriculate (native) === J. tenageia

6. Capsule ellipsoid. Flowers solitary or in groups of 2-3. Leaf sheaths never auriculate === 7

7. Tepals with a conspicuous dark line on either side of midrib. Seeds longitudinally ridged. Anthers 1,2-2 mm long. Leaves usually more than 1,5 mm wide === J. foliosus

7. Tepals without a dark line on either side of midrib. Seeds (almost) smooth. Anthers usually 0,4-1,2 mm long. Leaves usually less than 1,5 mm wide (native) === J. ambiguus and J. bufonius

8. Bracts much exceeding the inflorescence. Tepals acute, more than 3 mm long === J. tenuis

8. Bracts shorter or equaling (rarely slightly longer than) the inflorescence. Tepals obtuse, less than 3 mm long (native) === J. compressus and J. gerardii

9. Annual, plant easily uprooted. Usually rather small plants, rarely exceeding 30 cm (native) === J. bulbosus, J. capitatus and J. pygmaeus

9. Perennial. Usually taller plants, often more than 30 cm === 10

10. Seeds large, 1,1-2 mm, conspicuously tailed === J. canadensis

10. Seeds small, usually 0,4-0,7 mm (up to 0,9 mm in J. squarrosus), not conspicuously tailed, at most apiculate (native) === J. acutiflorus, J. alpinoarticulatus, J. anceps, J. articulatus, J. bulbosus, J. squarrosus and J. subnodulosus

Additional aliens: Juncus imbricatus Laharpe (S-Am., wool alien), J. pallescens Lam. (S-Am., wool alien), J. radula Buchen. (Austr., wool alien) and J. subsecundus N.A. Wakef. (Austr., wool alien).

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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. [available online at: http://speciesplantarum.net/sites/alienplantsbelgium.bedefault/files/flo... http://speciesplantarum.net/sites/alienplantsbelgium.bedefault/files/flo... http://speciesplantarum.net/sites/alienplantsbelgium.bedefault/files/flo... ] 

Kirschner J. (2002b) Species Plantarum. Flora of the world. Juncus subg. Agathryon. Vol. 8(3). Australian Biological Resources Study, Canberra: VIII + 192 p. [available online at: http://speciesplantarum.net/sites/alienplantsbelgium.bedefault/files/flo... http://speciesplantarum.net/sites/alienplantsbelgium.bedefault/files/flo... http://speciesplantarum.net/sites/alienplantsbelgium.bedefault/files/flo... http://speciesplantarum.net/sites/alienplantsbelgium.bedefault/files/flo... ]

Lambinon J., Delvosalle L., Duvigneaud J. (avec coll. Geerinck D., Lebeau J., Schumacker R. & Vannerom H. (2004) Nouvelle Flore de la Belgique, du Grand-Duché de Luxembourg, du Nord de la France et des Régions voisines (Ptéridophytes et Spermatophytes). Cinquième édition. Jardin botanique national de Belgique, Meise: CXXX + 1167 p.

Mabberley D.J. (2008) Mabberley’s plant-book (3th ed.). Cambridge University Press, Cambridge: XVIII + 1021 p.

Snogerup S. (1980) Juncus. In: Tutin T.G. & al. (eds.), Flora Europaea, vol. 5. Cambridge University Press, Cambridge: 102-111.