Alien plants can come in in various ways. Well known examples of inadvertent introductions are, for instance, weedy species that are introduced as contaminants in cereals (so-called grain aliens) or pasture species that are introduced in sheep wool (so-called wool aliens). Likewise, the nursery trade is also responsible for the introduction and spread of weed species. Other sources may be bark or timber, granite, coal, sand, etc. but these vectors are obviously of a lesser importance in Belgium than are cereals these days or was wool in the past.
In 2015 a new peculiar vector for the introduction of alien plants was met with along the Belgian coast: several interesting thermophilous, psammophilous species from southern Europe were found growing in camping sites, some apparently never recorded before in Belgium. Although not widely so, campsites are known to often harbor an interesting non-native flora but there seem to be no studies that thoroughly investigated the issue (for some, very fragmented information, see e.g. Vivant 1983, Woodhead & Clement 1997). These species – often with spiny, hooked or bristled fruits and/or with tiny seeds – had obviously been introduced unintentionally with tourists coming from southern Europe (adhered to car mats, tents and other camping equipment). In 2016 campings, caravan parks and similar localities were visited in a more systematic way and it seems that this introduction vector is more important than initially admitted. Numerous aliens seem to have arrived in Belgium this way and many of them look perfectly naturalized (at least locally) and may start spreading in a near future, away from the original place of introduction.
A detailed account will be published in Dumortiera (see also Verloove 2016). In this note some preliminary results are already presented. It also aims at encouraging botanists to inspect similar places in search for these alien plants. Although circumstances are perhaps more favorable in the climatologically milder coastal areas, several of the species here concerned have also been found in inland campings (e.g. Jabbeke, Gent). Other habitats that may harbor the same array of species are golf courts, football- or cricket fields, etc.
Overview of some of the more interesting taxa observed so far (as per 20 May 2016):
Ranunculus muricatus L.
A very rare alien in Belgium. A small population with scattered individuals was found in a camping in Nieuwpoort in 2016.
Ranunculus parviflorus L.
A very rare alien in Belgium. This species was known so far from De Panne where it is naturalized as a lawn weed in a cemetery near the coast (at least since the 1950’s). It is an occasional weed elsewhere, for instance in the Botanic Garden in Meise. In 2016 this species was observed in several campings (e.g. Blankenberge, Bredene, Nieuwpoort, Wenduine), also in inland localities (Gent).
Medicago littoralis Rohde ex Loisel.
Never recorded before in Belgium. Few plants were seen in a camping in De Panne in 2015 and confirmed in 2016. Similar records from campings in coastal areas in northwestern France were already known (Lambinon & Verloove 2012).
Several other species of Medicago have also been recorded, e.g. M. polymorpha L., M. cf. praecox DC., M. truncatula Gaertn., as well as the native species M. arabica (L.) Huds. and M. minima (L.) Bartal.
Trifolium nigrescens Viv.
Never recorded before in Belgium (previous claims turned out to be referable to T. michelianum). A small population was detected in 2016 in a camping in De Panne.
Trifolium suffocatum L.
Never recorded before in Belgium. Discovered in 2015 in a camping in De Panne and confirmed in the same locality in 2016. This species has very inconspicuous flowers and easily passes unnoticed. At least 8-9 subpopulations were counted, some with more than 100 individuals. In identical circumstances also found in an inland camping in Gent. Similar records from campings in coastal areas in northwestern France were already known (Lambinon & Verloove 2012).
Trifolium tomentosum L.
A very rare alien, usually associated with wool importation (Verloove 2006). A beautiful population with several tens of plants was found on nearly bare sand in a camping in De Panne in 2015 and confirmed in 2016.
Parentucellia latifolia (L.) Caruel
Never recorded before in Belgium. Discovered in 2016 in campings in De Panne and Nieuwpoort. In the first locality a small population with 15-20 individuals, possibly more or less established or tending to become so.
Galium murale (L.) All.
Recorded at the beginning of the 20th century in Belgium (Verloove 2006) and lately increasingly observed in urban habitats (e.g. Anwerpen, Brugge, Gent). In 2016 discovered in campings in Blankenberge and Heist. In the first locality the species occurs with many hundreds of individuals and is obviously naturalized.
Cotula australis (Sieber ex Spreng.) Hook. f.
Formerly a characteristic but fairly rare wool alien in the Vesdre valley near Verviers, between 1893 and 1921 (Verloove 2006). In 2015 found again as an urban weed in the city of Brussels. In 2016 found in several campings, all at the Belgian coast (e.g. Blankenberge, De Haan, De Panne, Lombardzijde, Nieuwpoort, Wenduine, Westende). In some localities very common and obviously naturalized.
Soliva pterosperma (Juss.) Less.
Formerly recorded as a characteristic but rather rare wool alien in the Vesdre valley near Verviers, between 1887 and 1904 (Verloove 2006). This South American species first naturalized in southern Europe and lately started traveling further north (e.g. Woodhead & Clement 1997). Its presence in campings in Belgium was expected and, indeed, in 2016 it was found on several instances (e.g. Blankenberge, Bredene, De Panne, Nieuwpoort, Wenduine), also in inland campings (e.g. Gent, Jabbeke). In some places it forms nearly monospecific mats with thousands of individuals; it either must have been introduced some time ago or reproduces very fast. The sharp spine. a persistent style in origin, on top of the achene pierces foot wear and car tyres!
Poa infirma Kunth
Never recorded before in Belgium. Discovered in 2016 in several campings (e.g. Blankenberge, Bredene, Nieuwpoort, Wenduine) and doubtlessly widely overlooked elsewhere. Also seen in an inland camping (Gent). This species is much reminiscent of our common native species Poa annua. In most places it occurs with numerous individuals and is obviously naturalized, at least locally. A further spread, especially in coastal areas, is very likely.
Other interesting records include, among others, Capsella rubella (common), Crassula tillaea, Erodium moschatum, Filago pyramidata, Polycarpon tetraphyllum, Rostraria cristata, Scleranthus annuus subsp. polycarpos, Trifolium micranthum, T. resupinatum, T. subterraneum, etc. Some of these are native species but may be considered introductions in camping sites.
LAMBINON J. & VERLOOVE F. (avec coll. Delvosalle L., Toussaint B., Geerinck D., Hoste I., Van Rossum F., Cornier B., Schumacker R., Vanderpoorten A. & Vannerom H.) (2012) Nouvelle Flore de la Belgique, du Grand-Duché de Luxembourg, du Nord de la France et des Régions voisines (Ptéridophytes et Spermatophytes). Sixième édition. Jardin botanique national de Belgique, Meise: CXXXIX + 1195 p.
VERLOOVE F. (2006) Catalogue of neophytes in Belgium (1800-2005). Scripta Botanica Belgica 39: 89 p. [available online at: http://alienplantsbelgium.be/sites/alienplantsbelgium.be/files/tabel_2.pdf]
VERLOOVE F. (2016) Les campings du littoral belge: un lieu de prédilection inattendu pour l’introduction de plantes exotiques. Natura Mosana 69(1-2) (in print).
VIVANT J. (1983) Brèves notes sur la flore adventice. Bull. Soc. Bot. France. Lettres Botaniques, 130(1): 81-83. [available online at: http://www.tandfonline.com/doi/abs/10.1080/01811797.1983.10824573]
WOODHEAD F. & CLEMENT E.J. (1997) Soliva pterosperma established at Bournemouth. BSBI News 76: 56 and front cover. [available online at: http://archive.bsbi.org.uk/BSBINews76.pdf]