Eruca vesicaria (L.) Cav. (Medit.) – A rather rare but possibly overlooked, usually strictly ephemeral alien. Apparently known in the wild in Belgium since at least 1837 (Verloove 2006) and still seen every year in rather numerous localities. Eruca vesicaria easily self-seeds in gardens and sometimes can persist locally for some years.
In the past decades Eruca vesicaria was mostly associated with imported cereals and often seen in abundance on unloading quays, by roadsides, on railway yards, etc.
Eruca vesicaria is somewhat reminiscent of Raphanus raphanistrum in general appearance. However, its siliqua splits longitudinally and has a conspicuous flattened beak (hence its Dutch vernacular name, Zwaardherik).
Most if not all records refer to what is sometimes segregated as subsp. sativa (Mill.) Thell. (syn.: E. sativa Mill.). These plants have broader leaf segments and early deciduous sepals. However, molecular studies (Warwick & Black 1993) support the treatment of subsp. vesicaria and its presumed derivative subsp. sativa as a single species.
Selected literature:
Schnedler W. (1977) Pflanzen, von denen in der mitteleuropaischen Literatur setten oder gar keine Abbildungen zu finden sind: Folge I. Eruca sativa, Eragrostis tef, Solanum rostratum, S. sisymbrifolium, S. sodomaeum. Gött. Flor. Rundbr. 10(4): 85-91.
Verloove F. (2006) Catalogue of neophytes in Belgium (1800-2005). Scripta Botanica Belgica 39: 89 p. [available online at: http://alienplantsbelgium.be/sites/alienplantsbelgium.be/files/tabel_2.pdf]
Verloove F. & Vandenberghe C. (1995) Nieuwe en interessante voederadventieven voor de Belgische en Noordfranse flora, hoofdzakelijk in 1994. Dumortiera 61-62: 23-45. [available online at: http://alienplantsbelgium.be/sites/alienplantsbelgium.be/files/dum61-62p...
Warwick S.I. & Black L.D. (1993) Molecular relationships in subtribe Brassicinae (Cruciferae, tribe Brassiceae). Can. J. Bot. 71: 906-918.