Eleocharis is a large, cosmopolitan genus of ca. 200 species. Its greatest diversity is in (sub-) tropical America. At least six species are native in Belgium although some are very rare: Eleocharis acicularis (L.) Roem. et Schult., E. multicaulis (Smith) Desv., E. ovata (Roth) Roem. et Schult., E. palustris (L.) Roem. et Schult., E. quinqueflora (F.X. Hartm.) O. Schwartz and E. uniglumis (Link) Schult. (Lambinon & al. 2004).Several non-native species are introduced in Europe, especially in rice-producing areas (Italy, Portugal,…). They are sometimes hardly distinguished from related native species and might pass unrecorded. In Belgium two “new” species of Eleocharis were discovered in 2006: E. austriaca Hayek and E. obtusa (Willd.) Schult. (Lambinon & Mause 2010). They closely resemble Eleocharis palustris (or E. uniglumis) and E. ovata respectively and are opposed to these native species in the couplets beneath.

Eleocharis palustris-group

1. Only lowest glume of spikelet empty, encircling base of spikelet (native) === Eleocharis uniglumis

1. Two lowest glumes of spikelet empty, each half encircling base of spikelet === 2

2. Stylopodium (swollen style base) at least twice as long as wide, slightly constricted at base. Perianth bristles usually 5 (4-6). Anthers 1,7-2,2 mm. Stem weak, easily cracked === E. austriaca

2. Stylopodium slightly longer than wide, distinctly constricted at base. Perianth bristles usually 4 (rarely 0). Anthers 2,1-3,5 mm. Stem pliable but not easily cracked (native) === E. palustris

Eleocharis ovata-group

1. Stem up to 2 mm wide, often robust, 3-50(-90) cm. Stamens usually 3. Stylopodium ca. as wide as nut, 0,5-0,9 mm wide === 2

1. Stem up to 1 mm wide, often more slender, 2-35 cm. Stamens usually 2. Stylopodium ca. 2/3 as wide as nut, 0,3-0,5 mm wide (native) === Eleocharis ovata

2. Stylopodium 1/3–1/2 as high as achene, at least 2/3 as high as wide. Perianth bristles slightly to (usually) much exceeding stylopodium. Most styles 3-fid === E. obtusa

2. Stylopodium not more than 1/4 as high as achene, 1/10-2/5 as high as wide. Perianth bristles rudimentary to at most equaling stylopodium. Most styles 2-fid === E. engelmannii

Selected literature:

Foerster E. (1972) Die Gattung Eleocharis. Gött. Flor. Rundbr. 6(4): 96-101.

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.

Lambinon J. & Mause R. (2010) Deux Eleocharis (Cyperaceae) nouveaux pour la flore belge: E. austriaca et E. obtusa au Camp d’Elsenborn (Haute-Ardenne). Dumortiera 98: 1-5.

Smith S.G., Bruhl J.J., González-Elizondo M.S. & Menapace F.J. (2002) Eleocharis. In: Flora of North America Editorial Committee (eds.), Flora of North America, vol. 23. Oxford University Press, New York-Oxford: 60-120.

Stace C. (1997) New flora of the British Isles, 2nd ed.: XXVII + 1130 p. Cambridge University Press.

Walters S.M. (1980) Eleocharis. In: Tutin T.G. & al. (eds.), Flora Europaea, vol. 5. Cambridge University Press, Cambridge: 281-284.

Taxonomic name: 
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith