My copy of The Englishman's Flora (Geoffrey Grigson) lists dozens of alternative names for this common plant, from the pretty Rutland Beauty, Shimmy-and-Buttons and Robin-run-the-Hedge,to the sinister Devils Garter, Strangleweed and Devil's Guts.
A name not in the book is the one my mother taught - Granny Pop the Bed - so called because if you squeeze the green base of the trumpet shaped head (see photo 2) the white flower pops out. It's not a very convincing pop it has to be said, but hey, when you're six its great!
In the jargon, the green flower base is called the calyx (I've labelled this in photo 2). The 'leaves' that make it up are called sepals. C.sepium also has an outer epicalyx.
When I first started this posting I took it for granted that a web search would turn up scores of scientific papers on my common weed. As it turned out I struggled to find any! I did come across a research paper  on the apparently unusual lectin (a protein) biochemistry chemistry of my weed, but the subject matter was rather technical and I'm not expert enough to do it justice here. This aside most of the material I did manage to find concerned the related Field Bindweed (Convolvulus arvensis), a target for frequent study because it is a major weed of arable crops. (Field- and Hedge Bindweed can be readily distinguished by knowing that Field Bindweed doesn't have an epicalyx).
This lack of literature meant that for a time I was left wondering what to say in this post, but then I recalled an unusual fact concerning Bindweed's spiral growth which I'd read about some time ago (I don't remember where). Photo 1 shows a plant climbing a garden cane. As it climbs the stalk is seen to spiral in an anticlockwise direction (as viewed from above). What's interesting is that C.sepium always spirals anticlockwise. (I've even been around my garden checked! Indeed once you know this fact, its hard resist the temptation to check the spiral of every Hedge Bindweed you see anywhere!).
This feature of always twisting one way turned out to be rather a rich topic for exploration. Amongst others I was led to a paper by Thitamdee et.al.  on the origins of spiral forms in plants:
The authors' studies focused on plant microtubules. These are molecular sized rods found in both plant and animal cells (they've received mention on my blog before, here). Its been discovered that large numbers of these rods decorate the surface of plant cells (like matchsticks stuck on a balloon). The rods do not lie randomly on the surface of the cells however, rather they order themselves so as to line up along a common direction. There's some amazing video of real microtubules jostling about on cell surfaces on the webpage of Indiana University's Shaw Lab. here. Now, to continue the balloon analogy, imagine having a lot of matchsticks densely glued to the surface of one of those sausage shaped party balloons. Imagine the matches are all lined up so as point around the short, circular axis of the balloon (like hoops around a barrel). Next, imagine blowing more air into the balloon. Though I haven't actually done the experiment, I hope its reasonable to suggest that the rigid matches would make it more difficult for the balloon to swell in circular cross-section (get 'fatter'), and instead the balloon would grow more freely lengthwise (get longer). This is exactly what aligned microtubules are believed to do for plant cells i.e. cells that would otherwise grow and expand as simple spheres are instead constrained to grow and expand along a preferred direction. This is useful because it allows the plant to create e.g. long, thin cells suitable the plant stalk. (Actually, strictly its not microtubles themselves that constrain the growth of the cell walls, rather the microtubles appear to act as markers for the laying down of a secondary stiffening material - cellulose - but the principle's the same)
Now, Thitamdee et.al. were studying a cress plant called Arabidopsiss. This is famous amongst botanists as the plant for genetic studies worldwide. Normal Arabidposis plants don't spiral, they grow straight. Furthermore, when scientists looked at the microtubules on cells in the stalk they found them to be arranged exactly as in the description above (i.e. 'hoops around a barrel')
What Thitamdee et.al. discovered however, was that a mutation in a single gene can cause a change in the way microtubles on cells in the stalk of an Arabidopsis plant arrange themselves. Specifically, they observed mutations that caused the microtubules to shift from being aligned all-parallel to the cell circumference ('hoops around a barrel') to instead all lying on the cell surface at an angle to the long axis of the cell.
And what did these mutant plants, with their slanted microtubles, do? Yep, grow in a spiral!
The importance of this work is that it implies an explanation for why some plants spiral and some don't, and furthermore why, for many species, every individual must spiral in the same direction: Things are dictated by the angle at which microtubles are aligned on the cells. This in turn is hardwired by the plant's DNA. Perhaps an ancient ancestor of Hedge Bindweed grew straight. At some point however a gene mutation arose that caused the microtubles to align at some new angle. With this angle fixed by the DNA, the Bindweed's fate was fixed; Subservient to the constraining forces acting on its cell walls, it was doomed to spiral, and always in the same direction, this being dictated by the angle of microtubule alignment (though what this is specifically I don't know - I haven't found any reference to suggest the microtuble alignment of C. sepium specifically has been studied).
To end, a bit of humble pie. When I first recognised the anticlockwise spiralling of Bindweed, I admit I thought I was rather clever in having uncovered some little known fact... until, that was, I discovered that my supposed 'little known fact' even had its own popular 1950's song!
The fragrant honeysuckle spirals clockwise to the sun,
And many other creepers do the same.
But some climb anti-clockwise, the bindweed does, for one,
Or Convolvulus, to give her proper name...
( from Misalliance by Flanders and Swann, ).
The Crystal Structure of the Calystegia sepium Agglutinin Reveals aNovel Quaternary Arrangement of Lectin Subunits with a Prism Fold, Y Bourne et.al., The Journal Of Biological Chemistry, 279(1),pp. 527–533, 2004
 Microtubule basis for left-handed helical growth in Arabidopsis, S. Thitamadee, K. Tuchihara & T. Hashimoto, Nature, 417, p.193, 2002.