Galium murale (L.) All. (Medit., SW-Eur) – A very rare but possibly overlooked alien. In 1902 recorded as wool alien in the valley of river Vesdre. More recently detected on several occasions in containers with olive trees from the Mediterranean in garden centers (Hoste & al. 2009). Persisting for some years (2010-2015) between cobble stones in Hooglede. In 2014 at least two populations have been discovered in the city of Gent (foot of walls, pavement, etc., and apparently well-established). In 2016 it was also seen for the first time in urban habitats in Brugge and in 2019 in Liège. Since 2016 large populations were detected in camping sites in coastal areas (Blankenberge, Heist, Koksijde,...). Although unmistakable, Galium murale is a very inconspicuous species and might easily pass unrecorded. It may well be more widespread, especially in urban areas and in coastal areas.
With its cylindrical mericarps, yellowish green corollas in few-flowered inflorescences, Galium murale cannot be confused with any of the other Belgian representatives of the genus, native as well as introduced.
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Selected literature:
Denters T. (2015) Flora op drift. Galium murale: een 'Straatwalstro'. Planten FLORON 2: 12.
Hoste I., Verloove F., Nagels C., Andriessen L. & Lambinon J. (2009) De adventievenflora van in België ingevoerde mediterrane containerplanten. Dumortiera 97: 1-16. [available online at: http://www.botanicgarden.be/DUMORTIERA/DUM_97/Dum%2097_1-16_Mediterrane%20containerplanten_Hoste%20et%20al.pdf]