Bindweeds
What are they?
The bindweeds form the bulk of the family Convolvulaceae. They are attractive plants with their showy, bell-shaped flowers, but several species have a reputation for being deep-rooted and very persistent weeds of gardens and agricultural land. The flowers consist of five petals, fused together to form a cone of thin, rather fragile petals. Most plants are climbers with twining stems, or trail across the ground, climbing when they find something to support them.
Where are they found?
Bindweeds are prolific growers and are most frequent on heavier, richer soils. The group is more or less easily divided into a handful of common and widespread species that are found in a wide range of habitats, plus a few species that are garden escapes and likely only to be found on rough ground or roadsides in urban areas.
Identification
A few species can be identified by their distinctive leaves, combined with their typical bindweed flowers. Others are less easy to tell apart and identification requires a look at the details of the flowers and their stems. The flowers have five sepals, but these are generally hidden beneath two, leaf-like bracts that surround the base of the flower. In the larger Calystegia species, the detail of these bracts separates the species, together with the presence or absence of hairs on the flower stalk. Note that all of the white species can also occur in pink, so flower colour alone should not be used for identification.
Field Bindweed Convolvulus arvensis
Native. A widespread and common plant on arable land and in gardens and rough ground, but also in dunes, grassy roadsides and even shingle beaches. Flowers mostly June to August but sometimes also outside of this period. Smaller than the Calystegia bindweeds and more likely to be creeping on open ground rather than climbing. Ten different colour forms of the flowers have been described, based on the amount of pink or white and the presence or absence of purple spots at the centre (three are illustrated here).
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Large Bindweed Calystegia silvatica
Originally introduced as a garden plant but strong-growing and difficult to control. Now widespread and common throughout most of our region, most often as a vigorous species that twines over fences and hedges and climbs up into trees in urban and suburban settings. Flowers mostly late July to September. Best told from Hedge Bindweed by the flower bracts, which broadly overlap each other, leaving the sepals almost completely hidden beneath them. The flower stalk is hairless. The variety quinquepartita is rare and has the five petals joined only at the base.
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Hedge Bindweed Calystegia sepium
Native in all kinds of wetlands, especially fens and reedbeds. In roadside ditches it can occur alongside Large Bindweed. Flowers mostly late July to September. Best told from Large Bindweed by the flower bracts, which are smaller, leaving a gap that clearly reveals the sepals beneath them. The flower stalk is hairless.
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Hairy Bindweed Calystegia pulchra
Introduced as a garden ornamental. Rare, but long-lived and the handful of sites where it occurs have been known for many years. Flowers July to September. Flowers pink with two lines of hairs running down the flower stalks. The hairs can sometimes be difficult to find and an easier identification feature is in the leaves, which are less shiny than Hedge or Large Bindweed and which have a square-sided gap between the two basal lobes, rather than a V-shaped gap. Flowr bracts large and strongly overlapping.
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Howitt's Bindweed Calystegia x howittiorum
A rare hybrid between Large and Hairy Bindweeds. Flowers July to September. Flowers pink with two, weak lines of hairs on the flower stalks. The leaves are typically intermediate between the parents, having the shiny look of Large Bindweed but with a relatively broad gap between the two basal lobes.
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Sea Bindweed Calystegia soldanella
Native in coastal sand dunes. Flowers June to August. Trails along the ground, often through Marram-grass clumps. Flowers rich, deep pink. Leaves kidney-shaped and slightly fleshy or succulent.
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Tricolour Bindweed Convolvulus tricolor
Introduced as a garden ornamental and occasionally found as a short-lived annual in urban areas on sown roadsides and borders. Flowers July to September. A low-growing, spreading plant rather than a climber. Leaves simple. Flowers richly coloure in blue, white and yellow.
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Common Morning-glory Ipomoea purpurea
Introduced from the Americas as a garden ornamental and occasionally appearing briefly where bird seed has been placed or spilt. Flowers July to August. A twining, annual, climber with flowers that open at night, remaining open into the day before closing by mid-morning. Closed flowers with rolled tops are thus more likely to be seen later in the day. Leaves broadly heart-shaped. Flowers deep bluish-purple, white or deep pink.
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Ivy-leaved Morning-glory Ipomoea hederacea
Introduced from the Americas and appearing from a variety of sources but never persisting. Flowers July to September. A twining, annual, climber with flowers that open at night, remaining open into the day before closing by mid-morning. Closed flowers with rolled tops are thus more likely to be seen later in the day. Leaves three-lobed, the upper leaves often simple. Flowers pale blue or becoming purple flushed as they wither.
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Small Kidneyweed Dichondra micrantha
Introduced from the tropics as a garden novelty and discovered as an established plant in dunes on the North Norfolk coast in 2021. Flowers May to September. A tiny, creeping plant with leaves rather similar to those of Sea Bindweed, but paler and less shiny. Flowers tiny, 2.5mm across, carried low amongst the 4-20mm leaves. The UK climate is unlikely to favour this tropical species, but elsewhere in tropical and warm temperate regions it is commonly grown as a ground-cover substitute for grass and has become an invasive weed in many countries.
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