9. Rumex pseudonatronatus Borbás (syn.: R. fennicus (Murb.) Murb., R. domesticus Hartm. var. pseudonatronatus (Borbás) Borbás) (N and E-Eur., C-As.) – An exceptional and ephemeral alien. A single plant was discovered on an unloading quay for cereals in Moen in 2010 (and subsequently confirmed in 2011). In 2011 furthermore seen under a grain conveyor in the port of Antwerpen (Amerikadok) (Verloove 2013).
Rumex pseudonatronatus is a more or less neglected species and possibly overlooked. It has some weedy tendencies and also occurs beyond its original distribution range, for instance in North America (Mosyakin 2005) or in parts of Scandinavia (Karlsson 2000). It was formerly recorded as a grain alien in the Netherlands as well (Danser 1917).
Rumex pseudonatronatus much looks like R. crispus and R. longifolius. With native Rumex crispus it shares the stature, the narrow leaves with distinctly crisped margins, relatively small valves with entire margins, etc. It is best distinguished by the total absence of tubercles on the valves. It has also been confused with Rumex longifolius. Both have valves with entire margins that lack tubercles, leaves with undulate margins, etc. However, Rumex pseudonatronatus has very narrow leaves (8-15x as long as wide) that taper at both ends and smaller valves. In general appearance, Rumex pseudonatronatus mostly looks like R. crispus while R. longifolius (with its wider leaves and often taller stature) is more reminiscent of a small R. patientia. It is not unlikely that Rumex pseudonatronatus has been overlooked in Belgium, especially at or near places where cereals are transported.
Danser B.H. (1917) Over Rumex fennicus, Rumex weberi en Rumex schreberi. Nederl. Kruidk. Arch. 1916: 161-176.
Karlsson T. (2000) Polygonaceae. In: Jonsell B. (ed.), Flora Nordica, vol. 1. The Bergius Foundation, Stockholm: 235-318.
Mosyakin S.L. (2005) Rumex. In: Flora of North America Editorial Committee (eds.), Flora of North America, vol. 5. Oxford University Press, New York-Oxford: 489-533.
Rechinger K.H. (1949) Rumices asiatici. Vorarbeiten zu einer Monographie der Gattung Rumex VII. Candollea 12: 9-152.
Verloove F. (2013) Verder onderzoek binnen het genus Rumex (Polygonaceae) in België. Dumortiera 102: 3-9. [available online at: http://www.br.fgov.be/DUMORTIERA/DUM_102/Dum_102_3-9_Rumex_Verloove.pdf]