Eleocharis engelmannii Steudel (N-Am.) – A very rare alien. A small population (ca. 30 individuals) was discovered on the exposed margins of a recently dug pond in the port area of Ghent in 2014 (Verloove 2015). In 2015 it was already found spreading to adjacent ponds, one more than 500 m away from the initial locality. It looks well-established in this locality. Also in 2015, Eleocharis engelmannii was found on the exposed banks of a recently built retention basin in Dadizele, along with Carex scoparia. Its presence was confirmed here in 2018. In 2017 E. engelmannii was also discovered on exposed pond margins in Marche-en-Famenne (Bois de Famenne). In 2018 +100 individuals were observed throughout this area. Up to present, this species was only recorded once before in Europe, i.e. in a military base in Germany (Heilbronn; Plieninger 2001).
Eleocharis engelmannii is much reminiscent of both E. obtusa and E. ovata and might have been overlooked in Europe. It shares the wide stylopodium (almost as wide as the nut) with E. obtusa, and it also is coarser than our native E. ovata (thicker and longer culms). From E. obtusa it is best distinguished by the lower stylopodium that is at most ca. ¼ of the length of the nut. Also, its perianth bristles are not longer than the stylopodium and most styles are 2-fid.
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Selected literature:
Brownell V.R., Blaney C.S. & Catling P.M. (1996) Recent discoveries of southern vascular plants at their northern limits in the granite barrens area of Lennox and Addington County, Ontario. Canad. Field-Nat. 110(2): 255-259. [available online at: https://archive.org/details/cbarchive_125880_recentdiscoveriesofsouthernvas1919]
Drapalik D. & Mohlenbrock R. (1960) A study of Eleocharis, Series Ovatae. Amer. Midl. Naturalist 64(2): 339-341.
Larson B.M.H. & Catling P.M. (1996) The separation of Eleocharis obtusa and Eleocharis ovata (Cyperaceae) in eastern Canada. Canad. J. Bot. 74: 238-242. [available online at: http://brendonlarson.com/wp-content/uploads/2013/04/Larson-and-Catling-1996-Eleocharis.pdf]
Plieninger W. (2001) Ein Fund von Eleocharis engelmannii Steudel bei Heilbronn. Ber. Bot. Arbeitsgem. Südwestdeutschland 1: 47-52. [available online at: http://www.botanik-sw.de/BAS/media/texte/Bericht_1.pdf]
Simons E.L.A.N., Wieringa J.J. & Gonggrijp S. (2020) Eleocharis ovata and its alien allies in the Netherlands. Gorteria 42: 28-35. [available online at: http://natuurtijdschriften.nl/search?identifier=712520]
Verloove F. (2015) Eleocharis engelmannii and E. obtusa (Cyperaceae), two recent acquisitions from sect. Ovatae in Belgium. Dumortiera 107: 25-30. [available online at: http://www.br.fgov.be/DUMORTIERA/DUM_107/Dum_107_25-30_Eleocharis%20Ovat... ]