Convolvulaceae (Bindweed Family)

Above: Convolvulus arvensis (Field Bindweed, Small Bindweed, Creeping Jenny) occurs naturally in some temperate regions but has been introduced and naturalised in most parts of the USA, parts of Africa and tropical regions, such that its distribution is now global.

Above and below: Convolvulus arvensis (Field Bindweed). This perennial herb is found in fields, cultivated ground, hedge-banks, roadsides and in waste places. The Convolvulaceae (Bindweed or Morning-glory family) are frequently climbers. C. arvensis is generally prostrate or trailing but is reported to climb when in shade and will then climb in a right-handed helix. This means that if you point the thumb of your right-hand in the direction of growth, towards the shoot apex, and curl your fingers round as if grasping the central axis, then the plant will follow the curl of your fingers, that is counterclockwise when viewed towards the base or clockwise when viewed towards the apex. This is dextral chirality. The other possible chirality (handedness) is left-handed (sinistral). Climbing plants are typically genetically programmed to twine with a given chirality.

The rootstock is creeping and gives out numerous slightly branched stems which twist and may climb to one meter in height. The alternate leaves (2.5 to 11 cm in length) are typically sagittate or hastate, that is triangular and arrow-shaped with the two basal lobes pointing outwards (hastate) or not (sagittate).

Inflorescence stems (peduncles) emerge from leaf/bract axils (axillary peduncles) and each bears either a single flower, with a single pair of bracts (secondary bracts or bracteoles) beneath or several in a cyme. (A cyme is a flowering axis with other axes branching off it, with many of the branches and the main primary axis ending in a flower.) In this case only the pedicels of the secondary flowers are accompanied by a pair of bracteoles, the flower on the primary axis being without.

The flower is pentamerous (has fivefold radial symmetry). The corolla (petal tube) is trumpet-shaped and pink to whitish with triangular red stripes and a yellowish base (presumably the yellow suggests pollen to pollinators). Five stamens with broad bases results in only five narrow channels at the base of the corolla leading to the nectar secreted around the base of the ovary. The anthers dehisce (split open) on their outer face, exposing pollen to any large-enough insect pushing past to reach the nectar. Dagger Flies (a family of dipterans or true flies) are reported to visit the flowers frequently and do have long mouthparts that could probably reach the nectar. The two stigma lobes are elongated and positioned to collect pollen from the backs of visiting insects.

The flowers are twisted in bud (convolute aestivation, aestivation referring to the folding of petals and sepals). There are two carpels, each two-celled (housing two ovules) and the fruit is a smooth capsule usually bearing 4 seeds and about the size of a large pea. The name Convolvula refers to the twining habit of the plant rather than the twisting of its floral parts in bud.

Calystegia

Calystegia sepium (Hedge Bindweed) and Calystegia silvatica (Large Bindweed), sometimes both called Large Bindweed can be distinguished by the pair of bracteoles enclosing the calyx of sepals. In C. sepium the bracteoles are slightly pouched and not or slightly overlapping at their sides. In C. silvatica the bracteoles are strongly pouched and strongly overlapping. these plants are twining perennials. C. silvatica is larger, reaching climbing heights of 3 m, occasionally up to 5 m, whereas C. sepium reaches climbing heights of 2, occasionally 3 m. Determination of species is by no means straightforward, however, as both quite readily hybridise to form C. x lucana = C. sepium x C. silvatica. This hybrid is quite common in parts of Britain, including the locale shown here (v.c. 15). Indeed, within the same hedge plants conforming to both parents could be found as well as intermediates 'Calystegia' means 'covered cup' (or 'covering cup'?) and refers to the bracteoles that cover the calyx.

This specimen, shown in both photos above, was determined as Calystegia silvatica. The bracteoles are tinged pink at the apex.

Above and below:this specimen was determined as C. sepium.

Above: C. sepium, below: C. silvatica.

Above: C. silvatica.

Calystegia sp.The two specimens below were not determined to species level.

Note the short stigmas compared to Convolvulus arvensis. The pollination mechanism of Calystegia is essentially the same as in Convolvulus, except that the larger flowers of Calystegia are visited more by larger insects, such as hoverflies and bumble-bees (especially Bombus pascuorum). Large hawk-moths, such as Sphinx convolvuli, has been reported as a visitor. The flowers only last one day, being replaced each day by the opening of new buds. Each flower opens soon after sunrise and many close by evening, having given up all its pollen, though some close the following day. Thus moths are not the chief pollinator but possibly contribute. Flowers will also close in dim light.

Calystegia has a creeping rootstock several mm in diameter, which is white, fleshy and brittle. The twisted stems twine in a right-handed manner. The leaves are cordate to hastate/sagittate at teh base. The axillary peduncles each bear a single flower. The large flowers are about 5 cm in diameter and the fruit capsules about half an inch (1.25 cm) across.

Above and below: festoons of Calystegia surrounding and growing up an Elder tree. This is one season's growth!

Below:buds and leaves of Calystegia sepium (unfortunately the camera lens needed cleaning)/

Other members of Convolvulaceae

Calystegia soldanella (Sea Bindweed) is a psammophyte (a plant that thrives in shifting sands) found on sandy seashores. Its rootstock is creeping and the stem procumbent and not climbing and not twisting and the leaves are fleshy. the capsule is about the size of a hazelnut.

The leafless twining parasitic Dodder, although sometimes placed in a separate family, is usually considered a member of the Convolvulaceae, based on molecular evidence. Another well known member of the family include the Sweet Potato (Ipomoea batatas).

Article created: 29 Dec 2020