Rumex is a surprisingly poorly known genus in Belgium, especially with regard to its non-native representatives.
Leonurus cardiaca subsp. villosus, a long forgotten and probably neglected xenophyte in Belgium
Dipsacus is a genus of ca. 15 Old World species, mainly distributed in Eurasia and the Mediterranean region (some in Africa and Asia). All species are more or less alike. However, a few are distinguished by shortly petiolate cauline leaves (not sessile and connate as in most other species) and globose flower heads. These are sometimes segregated as a distinct genus, Virga Hill. (see for instance Štepánek & Holub 1997) but this point of view is not followed by other recent taxonomists nor is it supported by molecular phylogenetic studies.
Bromus section Ceratochloa is a taxonomically complex assemblage of several different closely related taxa, all of New World origin. Especially Bromus carinatus and its relatives are notoriously difficult in terms of identification: some authors tend to accept a single variable species, others are convinced that several species merit species rank.
Petrorhagia (Ser.) Link is an Old World genus with ca. 33 species, ranging from the Canary Islands to Kashmir. One species, Petrorhagia prolifera (L.) P.W. Ball & Heywood, is native in Belgium although it often occurs in highly artificial habitats (by railway tracks, in gravel pits, on coalmine heaps, etc.) where it is most likely introduced. A second species, Petrorhagia saxifraga (L.) Link, has been recorded in Belgium as an ephemeral escape from cultivation. It is rather different in being a mat-forming perennial with flowers in lax cymes or solitary (vs.
Return of the aliens in 2011
In the past years the importance of garden escapes (deliberately introduced non-native plants that run wild) has steadily increased in Belgium (see Verloove 2006). "Genuine" aliens (unintentionally introduced non-native plants), on the contrary, have much decreased lately. Wool aliens are no longer seen since the 1970's in Belgium while grain aliens still occur but often in small amounts and confined to a restricted number of localities (mainly in port areas). An obvious explanation for this decline is lacking but one might think of the following:
In August 2011 I came across a dense population of a species of Lathyrus that I know since at least 25 years. It grows by a disused railway track and in adjacent grassland near Kortemark (prov. West-Flanders, Belgium; IFBL D1.26.41). It has always been referred to as Lathyrus latifolius L. and is mentioned as such on waarnemingen.be as well (see for instance http://waarnemingen.be/waarneming/view/55774177).
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.
The genus Cotoneaster has been thoroughly studied and documented in Belgium for more than 10 years now. In addition to one rather rare and local native species (Cotoneaster integerrimus Medik.) at least 24 additional, reliably identified non-native species are known to occur / to have occurred (see the updated Excel-version of the “Catalogue of neophytes in Belgium” on http://alienplantsbelgium.be/ for an overview). A few more require further study and confirmation.
Verloove (2008) reported about the discovery in 2001 of a well-established population of Inula racemosa Hook. f., a native of the western Himalayas, by a railway track near Kortrijk (Marke). In the very same area (Rollegem) a second, smaller population was furthermore discovered on an old dump in 2006. This species had long been confused with the exceedingly similar Inula helenium L.