Arable weeds

Source: Knapp, Alan. “Arable weeds.” Sussex Botanical Recording Society Newsletter, no. 62 (May 2006). http://sussexflora.org.uk/wp-content/uploads/2016/03/Newsletter_May_2006.pdf.

 

For most people, botanists and non-botanists alike, the sight of an arable field bright red with poppies is a real treat. Fortunately such fields can still be found somewhere in Sussex every year as the Common Poppy, Papaver rhoeas, which provides this spectacular display, is still reasonably common across most of the county.

However, many other arable weeds are among the most rapidly declining species in Sussex. If you want to get a feeling for the long-term changes it is very illuminating to look at the comments in the early Sussex floras by Arnold and Wolley-Dod.  One of the most dramatic examples is the Corn Buttercup, Ranunculus arvensis. In his 1887 Flora of Sussex, Arnold dismisses it in two words ‘Cornfields – com.’ and the situation was similar at the time of Wolley-Dod’s 1937 Flora, where it merits a few more words ‘Cornfields – common or rather common, and locally abundant on light soils’. By the time of the Sussex Plant Atlas, for which the survey covered the period 1966 to 1978, it was described as ‘Now only occasional’ but there are records from 66 tetrads. Compare this to the current situation where we have only 4 records from 2000 onwards, one of which was for a single plant, and the huge change becomes clear.

Admittedly Corn Buttercup is an extreme case, but it is not alone, and other arable weed species, while not suffering quite so badly, still appear to be declining rapidly. In order to learn more about this decline, and also to ensure that we get a good picture of the distribution of these species for our new Flora, we would like to ask you to keep a special look out for arable weeds, and in particular those listed below, as they are those which are either declining fast or are already rare. If you find a really good arable field with either some rare species or a good variety of more common species, could you please let one of the recorders or another SBRS committee member know about it (please do so when you find it, don’t wait until you send your records in).

One thing worth noting when recording arable weeds is that they are notoriously variable in numbers from year to year depending on exactly how a field has been cultivated. They are affected by the type of crop, time of ploughing, use of herbicides etc.. So, if there are arable fields in areas you are surveying for the flora, do try to go back and look at them in several different years and also look in the odd corners and bare patches as, with luck, you may be rewarded by finding something special.

Below is a list of species which are or may be declining, so we’d like you to keep a special eye out for them. Those species with a (*) after their name are often components of arable seed mixtures which get planted, so beware, especially if you see more than one of them together.

Apparently extinct in Sussex but could possibly survive somewhere

Ajuga chamaepitys (last seen on the downs above Denton, E.Sussex, where suitable habitat still exists)

 

Extremely rare and possibly on the point of extinction

Agrostemma githago(*), Anthemis arvensis (*), Fumaria vaillantii, Ranunculus arvensis,  Scleranthus annuus, Torilis arvensis.

 

Very rare or very rapidly declining

Adonis annua, Apera spica-venti, Centaurea cyanus (*), Filago lutescens, Fumaria densiflora, Fumaria parviflora,  Misopates orontium, Myosurus minimus, Scandix pecten-veneris.

 

Rare and/or declining

Anthemis cotula, Chrysanthemum segetum, Euphorbia platyphyllos (very variable in numbers from year to year), Filago vulgaris, Lamium hybridum, Lithospermum arvense, Papaver argemone, Papaver hybridum, Petroselinum segetum (rare as an arable weed away from the coast), Silene noctiflora, Valerianella dentata, Valerianella locusta, Veronica agrestis (especially in W. Sussex).

Note that both Valerianella species may have been over-recorded in the past – please look very carefully at the fruits to be sure it is not V.carinata and preferably send a specimen with fruit present to the Recorders.

 

Rather local (or possibly under-recorded) and declining, at least in some areas.

Aphanes australis (key out carefully to distinguish from its much commoner relative, Aphanes arvensis), Chaenorhinum minus, Euphorbia exigua (large decline off the chalk), Legousia hybrida, Lithospermum officinale, Papaver dubium subsp. dubium, Papaver dubium subsp. lecoqii, Ranunculus sardous, Spergula arvensis, Stachys arvensis, Thlaspi arvense.