1. Ornithopus compressus L. (Medit., Macaronesia) – A rare and usually ephemeral alien. Known from rather few locations. Discovered in 1882 on a canal bank in Oelegem and in sandy arable land in Wilsele in 1904. Also recorded at the railway station at Vierset-Barse in 1914. However, Ornithopus compressus is by far best known from Diest. It was repeatedly seen on and near the old city walls, at least between 1882 and 1891 (Pâque 1883, Ghysebrechts 1885). In 2004 it re-occurred in small number in the very same locality and has subsequently been confirmed regularly, the last time in 2007 (comm. P. Hendrickx 2019). It seems most vigorous when climatological circumstances in April are favourable (i.e. hot and dry). Ornithopus compressus grows on a steep off-ramp with southern exposure at the citadel. The species most likely emerged from a long-buried seed bank. In some years it is not seen at all but it seems to be a component of the local permanent seedbank. In 2019 it was also discovered in a more natural habitat, in a military base in Koersel.
In the Netherlands Ornithopus compressus has also been recorded in recent years (also on sandy, sun-exposed slopes) but it was not able to become naturalised (Reijerse 1996).
Ghysebrechts L. (1885) Nouveaux renseignements sur la florule des environs de Diest. Bull. Soc. Roy. Bot. Belg. 24: 38-55.
Lienenbecker H. & Raabe U. (1980) Pflanzen von denen in der mitteleuropäischen Literatur selten oder gar keine Abbildungen zu finden sind, folge 12. Ornithopus compressus. Gött. Florist. Rundbr. 14: 9-12.
McClintock D. (1969) Ornithopus compressus. Bull. Kent Field Club 14: 51.
Pâque E. (1883) Nouvelles recherches sur la flore belge. Bull. Soc. Roy. Bot. Belg. 22: 29-43.
Reijerse F. (1996) Ornithopus compressus L. (Geel vogelpootje) in Noord-Limburg. Twee vindplaatsen dicht bijeen en toch onafhankelijk. Gorteria 22: 97-100.