Agrostis scabra Willd. (N-Am., NE-As.) – Naturalised in the port of Antwerpen, at least since the 1990’s (but possibly since the 1950’s; see Delvosalle 1953). Mostly found in disused railway yards, sandy road verges or vacant lots in port areas and other man-made habitats. Many of the largest populations have been destroyed in recent times but Agrostis scabra still persists locally. Also present on sandy arable land in the nature reserve Hageven between Hamont-Achel and Neerpelt, at least since 1967 (initially mistaken for native Agrostis canina and later also erroneously ascribed to Agrostis nebulosa). Discovered in abundance near a former sand pit in Lommel-Sahara in 2007 and in Lommel-Balendijk in 2010. Recorded in a military base (Groot Schietveld) in Brecht in 1987 (again as Agrostis nebulosa) and in 2010 also in Klein Schietveld in Brasschaat. Obviously most widely distributed on bare sandy soils in the Kempen and surely still under-recorded. Occasionally recorded elsewhere in disused railway yards (Gent, Brussels,…). Finally, Agrostis scabra is sometimes seen as an ephemeral grain alien and was formerly also recorded as an exceptional wool alien in the Vesdre valley around Verviers. Agrostis scabra is poorly known and probably overlooked since it easily passes unrecorded.
The first Belgian records were erroneously ascribed to the exceedingly similar Agrostis hyemalis (Walter) Britton, Sterns et Poggenb. (Delvosalle 1953). The latter is a smaller species with spikelets 1,5-1,7 mm (vs. 2-2,7 mm), lemmas 1-1,2 mm (vs. 1,5-1,7 mm), anthers 0,2 mm (vs. 0,4-0,5 mm) and leaves less than 1 mm wide (vs. 1-3 mm wide). However, the occurrence of this taxon in Belgium is not excluded (see for instance Ryves & al. 1996) and immature plants of Agrostis scabra could key out to A. hyemalis. Plants from the nature reserve Groot Schietveld (between Brasschaat and Wuustwezel) exhibit more or less intermediate features. However, compared with reliably identified specimens of both species from North America they are eventually ascribed to Agrostis scabra. In addition to the characters cited before Agrostis hyemalis always seems to have glumes that are acute at apex while they are acuminate in A. scabra.
Agrostis scabra itself also is a very variable species. Awned and unawned forms exist but only plants of the latter seem to occur in Belgium. Two more or less distinct biotypes occur in Belgium. Most plants are densely tufted, with mostly basal, very narrow, often involute leaves (< 1 mm wide). However, some populations (for instance from a disused railway yard near Gent) are not densely tufted and furthermore characterised by more leafy stems with much wider, flat leaves (ca. 3-4 mm wide). Such plants closely resemble Agrostis clavata Trin., a native of northern Eurasia (mainly Siberia) that was recently detected (as a native) in North America as well (Harvey 2007). In Agrostis clavata glumes are equal and (nearly) smooth on the keel whereas A. scabra has unequal glumes that are scabrous on the keel (see Kurtto & Ulvinen 1987).
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