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Do all climbing plants such as my morning glory grow clockwise, and if so, why?

• Your questioner is fortunate in not having bindweed in their garden. A quick look would have shown it to spiral anticlockwise to the sun (that is, when looked at from below), as do all Convolvulus species. In contrast, honeysuckle spirals clockwise.

He is less fortunate in not being familiar with the work of the comic musical duo Michael Flanders and Donald Swann, specifically their song Misalliance, which describes these plants:

“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.”

The direction of twist isn’t derived from the shoot following the sun, nor is it different in the southern hemisphere. As the direction of turn is species-specific, it is likely to be genetic. In 2002, botanist Takashi Hashimoto showed that mutations in the genome of Arabidopsis thaliana caused clockwise spiral growth in root hairs that are normally straight. Similar mutations could be responsible for opposite helices.

“The direction of twist is not derived from the shoot following the sun. It is likely to be genetic”

The original mutation would have conferred an advantage on climbing plants, whichever way they coiled, giving them the ability to climb higher toward the sun on the stems of other plants. If there is a herbicide out there that can prevent this spiralling, I have a garden full of bindweed just waiting for it.

Norman Doidge, Newton Abbot, Devon, UK

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This article appeared in print under the headline “Clockwise”