Brassica juncea (L.) Czern. (S and E-As.) – A regular but poorly known, usually ephemeral alien. It was apparently first collected at the railway station in Gent in 1857. It was said to be naturalized around Wijgmaal, Herent and Wilsele between 1882 and 1896, mainly as an agricultural weed in beet fields and in waste land. It was formerly also sometimes recorded as wool alien in the valley of river Vesdre. However, most records are related with grain importation (incl. birdseed). As such, Brassica juncea is frequently seen along motorways (from spilled seed), on dumps and in port areas.
Brassica juncea is derived from a cross of B. nigra and B. rapa (Mabberley 2008). It is usually very inconspicuous and easily passes unrecorded. Confusion is most likely with Sinapis arvensis (see Rich & Jermy 1998).
The very similar but African species, Brassica carinata A. Braun (derived from B. nigra x B. oleracea), is probably sometimes overlooked in Belgium. It is usually more glaucous, has slightly longer sepals (7-10 mm versus 4,5-7 mm) and petals (up to 17 mm long), lowest leaves with 0-1 pair of lateral lobes (versus 1-3) and slightly narrower fruits (< 3,5 mm wide) (see Rich 1987, Stace 2010).
Selected literature:
An X.H., Chen B.Y. & Fu T.D. (2000) Preliminary studies on the origin of the Chinese mustard (Brassica juncea). Cruciferae Newsletter 22: 5-6. [available online at: https://www.brassica.info/info/publications/cn/crunews22.pdf]
Gladis T. & Hammer K. (1992) Die Gaterslebener Brassica Kollektion: Brassica juncea, B. napus, B. nigra und B. rapa. Feddes Repert. 103(7-8): 469-507.
Mabberley D.J. (2008) Mabberley’s plant-book (3th ed.). Cambridge University Press, Cambridge: XVIII + 1021 p.
Olsson G. (1960) Species crosses within the genus Brassica, 1. Artificial Brassica juncea Coss. Hereditas (Lund) 46: 171-223. [available online at: https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1601-5223.1960.tb03082.x]
Prakash S. (1973) Artificial synthesis of Brassica juncea Coss. Genetica 44: 249-263.
Rich T. (1987) Cabbage patch - III. B.S.B.I. News 47: 25-26. [available online at: https://archive.bsbi.org.uk/BSBINews47.pdf]
Rich T.C.G. (1988) Brassica juncea (L.) Czern. & Coss./Sinapis arvensis L. Plant Crib 1988: 22.
Rich T.C.G. & Jermy A.C. (eds.) (1998) Plant crib. BSBI, London: 391 p.
Schnedler W. (1977) Pflanzen, von denen in der mitteleuropaischen Literatur selten oder gar keine Abbildungen zu finden sind: Folge 4.2: Drei Senf-Arten: Sinapis alba L., Brassica juncea (L.) Czern. und Brassica nigra (L.) Koch. Gött. Flor. Rundbr. 11(4): 92-95.
Stace C. (2010) New flora of the British Isles, 3th ed.: XXXII + 1232 p. Cambridge University Press.
Vaughan J.G., Hemingway J.S. & Schofield H.J. (1963) Contributions to a study of variation in Brassica juncea. J. Linn. Soc., Bot. 58: 435-448.