A small but apparently well-established population of Rumex kerneri was recently discovered in the port-area of Gent (E-side of Kennedylaan, km 11.8-11.9, little N of the Texaco petrol station; IFBL C3.53.14). Several tens grow in a grassy bank between the roadside and a railway track (see photos). The species is rather reminiscent of Rumex patientia L. and might have been overlooked. Both might furthermore be confused with Rumex cristatus DC., an increasing species in neighbouring countries but apparently not yet recorded in Belgium.
These three species have large, nearly orbicular fruiting valves at maturity (ca. 8 mm wide and long) and are distinguished in the following key that is based on Rechinger 1933, Rechinger 1964, Stace 2010 and own observations:
1 Valves with entire margins. Middle lateral leaf veins arising at ca. 45-60° from midrib. Leaves cuneate to truncate at base. Plant up to 200 cm tall, usually with a reddish stem. Largest tubercle much less than 1/2 valve width === Rumex patientia
1 Valves minutely denticulate, at least in the lower half (dents ca. 0,5-1 mm long). Middle lateral leaf veins arising at ca. 60-90° from midrib. Leaves slightly cordate at base. Plant variable in stature, usually with a green stem. Largest tubercle ca. 1/2 as wide as valve (or wider) === 2
2 Plant usually not exceeding 100 cm. Leaves with numerous glassy papillae on the veins beneath. Valves with minute dents up to 0,5 mm long === Rumex kerneri
2 Plant usually well exceeding 100 cm and often up to 200 cm tall (like R. patientia). Leaves without papillae on the veins beneath. Valves with more distinct dents up to 1 mm long === Rumex cristatus
Rumex kerneri is native in a rather small area from Hungary and Romania to Central Greece (Albania, Bulgaria, Greece, Hungary, former Yugoslavia and Romania according to Rechinger 1964). It is known since long as an established xenophyte in Austria. More recently it was furthermore discovered in northern Italy where it is a fast-spreading (but possibly long-overlooked) alien. Useful illustrations and interesting additional information on its occurrence in Italy is provided by G. Galasso: http://www.comune.milano.it/dseserver/webcity/Documenti.nsf/d38e0f65f96d36fc0125690e00465e37/8b5014ad6b13935dc1257638004f04c1/$FILE/Rumex_kerneri.pdf and http://www.comune.milano.it/dseserver/webcity/Documenti.nsf/0/e0319daa2639089dc125750d00298954/$FILE/Le_specie_alloctone_Poster_Galasso.pdf
It is now probably recorded for the first time in western Europe (there are apparently no records from the British Isles, France, Germany, the Netherlands, the Nordic countries, etc.).
A more detailed account on Rumex kerneri and other critical/rare non-native taxa of Rumex in Belgium will be published in a future issue of Dumortiera. In the meantime Belgian botanists are encouraged to critically look at Rumex patientia-like plants.
Rumex patientia itself also is a variable species. Its variation in Belgium should be critically assessed. Three subspecies are usually distinguished:
1 Valves longer than wide === subsp. recurvatus
1 Valves ca. as wide as long === 2
2 Stem usually reddish === subsp. patientia
2 Stem greenish white === subsp. orientalis
The usual (unique?) taxon in Belgium seems to be subsp. patientia while subsp. orientalis (Bernh.) Danser is the commoner one in the British Isles (Stace 2010). Subsp. recurvatus (Rech.) Rech. fil. is a rather local taxon and less likely to occur as an alien in western Europe.
Rechinger K.H. (1933) Vorarbeiten zu einer Monographie der Gattung Rumex, 2. Die Arten der Subsektion Patientiae. Feddes Repert. 31: 225-283.
Rechinger K.H. (1964) Rumex. In: Tutin T.G. & al. (eds.), Flora Europaea, vol. 1. Cambridge University Press, Cambridge: 82-89.
Stace C. (2010) New flora of the British Isles, 3th ed.: XXXII + 1232 p. Cambridge University Press.
F. Verloove, May 2011