Filip Verloove, Meise Botanic Garden
I have been looking at weeds introduced as contaminants in cereal and oilseed shipments since the early 1990’s, so-called grain aliens. The composition of this rich alien flora largely depends on the areas from where the cereals (and their weeds) were introduced. As a result, the grain alien flora may considerably change from one year to another. For example, as a result of the sudden importation of large amounts of soybeans in Belgium from the 1980’s onwards, a lot of new weeds were found near grain mills in our main port areas (viz Anoda cristata, Cardiospermum halicacabum, Ipomoea sp. pl., Sicyos angulatus, Sida sp. pl., etc.). These were typical weeds of soybean fields that were much less frequently encountered in other types of agricultural crops.
In recent years some new grain aliens were observed in the Antwerp and Ghent port areas that raised some questions about their origin. They are briefly discussed hereunder.
Arctotheca calendula and Oncosiphon piluliferum
These are two weedy composites from South Africa. Both were recorded on several occasions near grain storages in Antwerp and Ghent in the past years, sometimes in relative abundance. Yet, cereals are very rarely (if ever) introduced from South Africa to Belgium… The former is naturalized in the western Mediterranean area (e.g. France, Spain, Italy) and thus – at least theoretically – our plants could have been introduced from this secondary area, a well-known area of origin for at least part of the cereals imported to our country. However, in Southern Europe Arctotheca calendula is naturalized in various kinds of open, sandy and disturbed coastal habitats but not in agricultural fields. The case of Oncosiphon piluliferum is even more striking and its identification was not straightforward. Attempts to identify this species with floras from Europe and the Middle East – suspected areas of origin of any Matricaria or Tripleurospermum-like weed – were unsuccessful. The plants certainly looked a lot like Tripleurospermum decipiens, a rare grain alien from Turkey, Russia, etc., but could not be this because of their clearly 4-lobed disc florets (vs. 5-lobed) and smaller achenes that lack the typical oil glands. With the Flora of North America (Barkley & al. 2006) they were eventually identified as Oncosiphon and more precisely as O. piluliferum, yet another weed from … South Africa, a region from where no cereals are imported!
A further search learnt that both Arctotheca calendula and Oncosiphon piluliferum have become major weed problems in the grain belt in Western Australia (e.g. Michael & al. 2010). Under the predicted climate change scenario Oncosiphon piluliferum was even thought likely to experience the greatest increase in severity in Western Australia (Michael & al. 2011). But do we really import cereals and oil seeds from such a remote country? Upon inquiry at the Cargill grain mill in the Antwerp port area it turned out that half of the year cereals and oil seeds (mainly rapeseed) were indeed imported from Australia and this shed some new light on other grain aliens found there in recent years (see below).
Asphodelus fistulosus and Trifolium michelianum
These are two predominantly Mediterranean species and only moderately weedy there. The latter, for instance, usually grows in wet meadows and by standing water (Coombe 1968); it is virtually unknown as a weed in its native area. Asphodelus fistulosus is more often seen in cultivated grounds in Southern Europe but it mostly is a species of dry, sandy or rocky, more or less natural habitats. Trifolium michelianum has regularly been recorded at the Cargill mill in Antwerp in the past years. Although its identification was straightforward, some doubt remained just because this species was believed to be non-weedy. Asphodelus tenuifolius had been recorded in Belgium only a few times, the last time almost a century ago (Verloove 2006). Several individuals of this species were seen in 2019, again at the Cargill mill in Antwerp. A quick search on the internet showed that both are indeed noxious agricultural weeds in Australia, doubtlessly the area of origin of these ‘Mediterranean’ species…
Interestingly and surprisingly, no native Australian weeds were seen in these area in the ports of Antwerp and Ghent which seems to suggest that in the Australian grain belt most weeds are introductions.
In the past decades the world has become a global village, not only in terms of interconnectivity via social media. As a result of intercontinental shipments goods and their stowaways are transported without geographical limits. This increasingly will lead to unexpected observations as shown above.
Barkley T.M., Brouillet L. & Strother J.L. (eds.) (2006) Asteraceae. In: Flora of North America Editorial Committee (eds.), Flora of North America, vol. 19-21. Oxford University Press, New York-Oxford.
Coombe D.E. (1968) Trifolium. In: Tutin T.G. & al. (eds.), Flora Europaea, vol. 2. Cambridge University Press, Cambridge: 157-172.
Michael P.J., Borger C.P., MacLeod W.J. & Payne P.L. (2010) Occurrence of Summer Fallow Weeds within the Grain Belt Region of Southwestern Australia. Weed Technology 24(4): 562-568.
Michael P.J., Yeoh P.B., Ota N. & Scott J.K. (2011) Climate Change Impacts on Agricultural Weeds in Western Australia. RIRDC Publication No. 11/059.
Verloove F. (2006) Catalogue of Neophytes Belgium (1800-2005). Scripta Botanica Belgica 39: 1-89.