Rumex cristatus DC. (syn.: R. graecus Boiss. & Heldr.) (SE-Eur., W-As.) – An exceptional alien. A single plant was seen on the unloading quay for cereals at the Amerikadok in the port of Antwerpen in 2011. In the past years additional records came to light (Verloove 2013).
Rumex cristatus is possibly overlooked in Belgium. Confusion is likely with Rumex xerubescens (R. obtusifolius x R. patientia) (see Verloove 2008), Rumex patientia and R. kerneri (see key for their distinction). Main diacritic features are: basal leaf midrib/vein angle 60–90º (vs. more often ca. 45-60° but sometimes also up to 90° in Rumex patientia) and fruiting valves shortly but distinctly toothed (vs. smooth to at most slightly erose in R. patientia). The related Rumex kerneri usually has shorter stems and leaf veins are distinctly papillose beneath. Moreover, in the latter only one tubercle is developed while in Rumex cristatus usually three (unequal) tubercles are present on the fruiting valves. As a rule, in Rumex cristatus valves are more distinctly toothed than in R. kerneri but this does not hold true for the plants seen thusfar in Belgium. Both species are obviously closely related and perhaps better united or accepted as subspecies (as proposed by Akeroyd & Webb 1991).
A hybrid with Rumex patientia (R. x xenogenus Rech.fil.) has been recorded in the British Isles (Kitchener 2002).
Rumex cristatus is spreading in parts of Europe, for instance in Germany (Hetzel & Meierott 2002) but mostly in France (Jauzein 1990) and Spain (Quesada & al. 2007). Outside of Europe also known from North America (Mosyakin 2005).
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Selected references:
Akeroyd J.R. & Webb D.A. (1991) Morphological variation in Rumex cristatus DC. Bot. J. Linn. Soc. 106: 103-104.
Atha D. (2018) First report of Rumex cristatus (Polygonaceae) for New York State. Phytoneuron 2018-48: 1–3. [available online at: http://www.phytoneuron.net/2018Phytoneuron/48PhytoN-RumexcristatusNY.pdf]
Hetzel G. & Meierott L. (2002) Rumex cristatus DC. in Würzburg – ein bemerkenswerter Neufund für Deutschland. Flor. Rundbr. 36(1-2): 1-9.
Jauzein P. (1990) Rumex cristatus DC. en France. Monde Pl. 437: 1-3.
Kitchener G.D. (2002) Rumex × xenogenus Rech. fil. (Polygonaceae), the hybrid between Greek and Patience Docks, found in Britain. Watsonia 24: 209–213
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.
Quesada J., Salazar C. & Pastor J. (2007) Rumex cristatus DC. (Polygonaceae) especie exótica en Andalucía (S. España). Lagascalia 27: 416-418.
Rechinger K.H. (1947-48) Beiträge zur Kenntnis von Rumex IX. Candollea 11: 229-241.
Verloove F. (2008) Twee miskende Rumex-taxa in België. Dumortiera 95: 4-8.
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]