1. Apera interrupta (L.) Beauv. (syn.: Agrostis interrupta L.) (Medit.) – A rather rare but locally abundantly naturalised alien. Perhaps first recorded around Nieuwpoort in 1818. In the 19th century sometimes seen as a weed of sandy arable land but probably always more or less ephemeral. Introduced through a wide range of vectors: formerly exceptionally seen as a wool alien, now perhaps mostly introduced with cereals and building materials (sand, gravel…). The naturalisation of Apera interrupta in Belgium is rather poorly documented. Up to the 1970’s it was rare and mainly ephemeral (Verloove 2002), although it was already repeatedly recorded in the first half of the 20th century in some coastal areas. In sea dunes in Nieuwpoort it seems to have been present since at least the 1930’s and records from the surroundings of De Panne are available since the 1950’s. However, its wider naturalisation probably started in the 1980’s (compare with Holverda & van der Meijden 1989), at first in the port areas of Antwerpen, Gent and Zeebrugge where it was found in dry and sun-exposed habitats: sandy ruderal places, railway yards, sand-raised sites, by roadsides, etc. (Verloove 2006). Furthermore locally naturalised in coastal dunes. Records from other regions are probably mostly ephemeral. In Wallonia Apera interrupta is much less frequent and only very locally naturalised, for instance on railway yards.
The exact residence status of Apera interrupta in western Europe remains more or less equivocal. In the British Isles, contrary to Tutin (1980), it is now believed to be locally native (Ryves & al. 1996), whereas Apera spica-venti is accepted as an alien. The latter, indeed, most likely was once introduced but is probably preferably considered as an archaeophyte.
The exceedingly similar Apera intermedia was once found as an ephemeral alien in Brussel in 1907. In general habit it is identical with Apera interrupta but the glumes are acuminate and shortly awned (vs. acute), the callus of the lemma is glabrous (vs. hairy) and anthers are up to 1,5 mm long (see illustration in Bor 1968). It should be looked for in port areas; its occurrence cannot be ruled out.
Selected literature:
Bank-Signon I. & Patzke E. (1985) Beitrag zur Gramineenflora Nordrhein-Westfalens: Apera interrupta. Gött. Florist. Rundbr. 19: 46-53.
Bank-Signon I. & Patzke E. (1986) Zur Soziologie von Apera interrupta. Tuexenia 6: 21-24.
Bor N.L. (1968) Gramineae. In: Townsend & al. (eds.), Flora of Iraq, vol. 9. Ministry of Agriculture, Baghdad: VI + 588 p.
Conert H.J. (1979) Über den Unterbrochenen Windhalm, Apera interrupta (L.) Palisot de Beauvois. Hessische Floristische Briefe 28(2): 22-30.
Conert H.J. (ed.) (1998) Gustav Hegi Illustrierte Flora von Mitteleuropa. Band I, Teil 3 Poaceae (3.Auflage). Parey Buchverlag, Berlin: XXVII + 898 p.
Holverda W.J. & van der Meijden R. (1989) Apera interrupta (L.) Beauv. (Stijve windhalm), een dwaalgast burgert in. Gorteria 15: 141-148.
Jung K.-D. (1991) Apera interrupta (L.) Palisot de Beauvois in Hessen. Hessische Floristische Briefe 40(4): 49-52.
Ryves T.B., Clement E.J. & Foster M.C. (1996) Alien grasses of the British Isles. BSBI, London: XX + 181 p.
Saintenoy-Simon J., Godefroid S. & Verhelpen B. (1995) Groupe Flore Bruxelloise. Notes floristiques relatives à la Région de Bruxelles-Capitale (1991-1993). Adoxa 6-7: 27-37.
Tutin T.G. (1980) Apera. In: Tutin T.G. & al. (eds.), Flora Europaea, vol. 5. Cambridge University Press, Cambridge: 172.
Verloove F. (2002) Ingeburgerde plantensoorten in Vlaanderen. Mededeling van het Instituut voor Natuurbehoud n° 20: 227 p.
Verloove F. (2006) Apera interrupta. In: Van Landuyt W., Hoste I., Vanhecke L., Van den Bremt P., Vercruysse W. & De Beer D., Atlas van de flora van Vlaanderen en het Brussels gewest. Instituut voor Natuur- en Bosonderzoek, Nationale Plantentuin van België en Flo.Wer: 147.