Trifolium squarrosum L. (syn.: T. panormitanum C. Presl) (S-Eur.) – A very rare and ephemeral alien. Recorded in 1990 in a private garden from birdseed waste in Slins. In 1995 also seen on a demolition site of a former horse artillery in Gent, along with numerous other southern European aliens (emerging from an exposed seed bank; see Verloove & Heyneman 2012). In 2019 a single individual was found on dredging sludge in Genk.
In Trifolium squarrosum the calyx tube is densely bulbous-hairy (contrary to T. scutatum Boiss. with which the plants from Gent were initially confused).
In France this species is now increasingly sown along with other clovers (Coulot & Rabaute 2014), also just at the Belgian frontier (Coulot & Rabaute 2015).
Selected literature:
Coulot P. & Rabaute P. (2014) Premiers compléments à la Monographie des Leguminosae de France. Monde Pl. 513: 3-15.
Coulot P. & Rabaute P. (2015) Premiers compléments à la Monographie des Leguminosae de France. Monde Pl. 516: 11-35.
Verloove F. & Heyneman G. (2012) Merkwaardige plantencollecties van twee antropogene zaadbanken in Gent (Oost-Vlaanderen, België). Dumortiera 100: 19-24. [available online at: http://www.br.fgov.be/DUMORTIERA/DUM_100/Dum%20100_19-24_Zaadbanken%20Gent-Verloove%20en%20Heyneman.pdf]