Ridolfia segetum (L.) Moris (syn.: Anethum segetum L.) (Medit., Macaronesia) – A very rare and ephemeral alien. Recorded as wool alien in the valley of river Vesdre in 1921 (Fabri & Lambinon 1991), subsequently on a dump in Wijnegem in 1953. Recorded as grain alien in the port of Antwerpen in 2001. Repeatedly seen since 2009 in a few localities: at first by a roadside in the port of Roeselare, subsequently near a paste mill in the same port area (confirmed in 2010). Finally, also observed every year, often in quantity, on the unloading quay for cereals at the Amerikadok in the port of Antwerpen (2009-2014).
All early records were initially ascribed to the very similar Anethum graveolens. Both are indeed much reminiscent (yellow-flowered annuals with finely dissected leaves) but easily distinguished as follows: Ridolfia has much smaller fruits (1,5-2,5 mm long vs. 5-6 mm long in Anethum). In the absence of fruits Ridolfia is distinguished by the absence of an anise-like smell and by its emarginate petals (rounded in Anethum).
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Selected literature:
Fabri R. & Lambinon J. (1991) Quelques ombellifères jadis adventices lainières dans la vallée de la Vesdre, inédites pour la flore belge. Dumortiera 49: 16-22. [available online at: http://alienplantsbelgium.be/sites/alienplantsbelgium.be/files/DUM49P16.pdf]
Reduron J.-P., Mathez J., Downie S.R., Danderson C.A. & Ostroumova T. (2009) Pseudoridolfia, nouveau genre d'Apiaceae découvert au Maroc. Acta Bot. Gallica 156(3): 487-500. [available online at: http://www.life.illinois.edu/downie/Pseudoridolfia.pdf]