St Nicks

Centre for nature and green living

September 2015: Spotlight on.. Bindweed

Field Bindweed

Field Bindweed

If you’re a gardener, the name sums it up: an irredeemable weed that’s more than a bit of a bind if you’ve taken over a plot where it’s well established. The thin but strong, flexible stems twine round any vertical support, potentially strangling other plants, and the deep roots produce rhizomes that enable the plant to colonize underground regardless of whatever seeds are produced.

Ironically, many of the gardeners trying to get rid of it are likely to be searching the catalogues for hardy, disease-resistant climbers that produce a long succession of showy flowers under a wide range of growing conditions. But then the closely related blue Morning Glory, grown in Britain as a tender annual, is a rampant weed in parts of Spain. Everything’s relative.

Five species of bindweeds, or convolvulaceae, are listed in general field guides, and three of them grow at St Nicks – two native and one introduced species.

Field Bindweed, Convolvulus arvensis, is a deceptively delicate-looking plant with arrow-head leaves and attractive pink or white trumpet-shaped flowers with a light vanilla scent. It prefers fairly open habitats where it seems equally happy scrambling along the ground at the edge of a path, or climbing into taller vegetation beside a hedge.

Hedge Bindweed (left) and Large Bindweed

Hedge Bindweed (left) and Large Bindweed

Hedge Bindweed, Calystegia sepium, thrives in hedgerows, scrub and virtually anywhere with a bit of light and something to climb. It has larger, more heart-shaped leaves and much bigger, pure white flowers. Large Bindweed, Calystegia sylvatica, was introduced as a cultivated variety in the nineteenth century. Why is anybody’s guess. It is so similar to C. sepium that it takes close inspection to tell them apart – in fact according to the Biological Record Centre’s online Atlas of Flora, it was only recognised as a separate species in 1948.

A fine specimen of sylvatica will have larger flowers than sepium, but the largest Hedge Bindweed flowers are larger than the smallest Large Bindweed flowers. Confused yet? The “easy” way to tell them apart is to look at the base of the trumpet, where a pair of bracts (technically bracteoles) encloses the flower. The bracteoles of Large Bindweed have a wide, puffy looking base, and they overlap. In Hedge Bindweed, they are narrower and tighter. They overlap very little or not at all, allowing pale green sepals to show in between. The snag is that it seems the two species hybridise so there are plenty of doubtful specimens to puzzle over.

Are Bindweeds of any use? Some sources claim that the leaves and roots are edible, and more to the point palatable, though the fact that they have been used as an effective purgative might discourage foragers from experimenting. There are other claims that they are emerging as a new source of anti-cancer drugs, but websites making such claims lack clear credentials. One thing is certain: the large varieties flower until late autumn, and insects, particularly hoverflies, love them.

Oh yes, and what about the right-handed honeysuckle and the left-handed bindweed? Well, Flanders and Swann did their homework, and the bindweeds do indeed twist anti-clockwise, the opposite direction to honeysuckle. For a glimpse of the science behind it, have a look at http://www.nature.com/news/2002/020509/full/news020506-6.html
With acknowledgement and thanks to Alison Jukes, who first pointed out that the white bindweeds at St Nicks were two species, not just one, and showed us how to differentiate them.

21 September 2015 | Categories: Spotlight on... | Tags: Bindweed, Field Bindweed, Hedge Bindweed, Large Bindweed