When it comes to twin­ing plants, Dar­win was right

Pop­u­lar mis­con­cep­tions about twin­ers were dis­proved back in the 19th cen­tury, cour­tesy of Charles Dar­win

The Daily Telegraph - Saturday - - GARDENING -

KEN THOMP­SON

twin­ing in the north­ern hemi­sphere and left-handed twin­ing in the south­ern hemi­sphere. Pre­dic­tions of the sun hy­poth­e­sis are more com­pli­cated, but you would still ex­pect the di­rec­tion of twin­ing to vary with hemi­sphere and lat­i­tude.

In 2007, New Zealand ecol­o­gist An­gela Moles pub­lished a pa­per show­ing that about 92 per cent of the world’s twin­ing plants twine in a right-handed helix, and this is true ev­ery­where on the planet, so both hy­pothe­ses are wrong, and hops are in the small left-handed mi­nor­ity. But Dar­win’s ob­ser­va­tions, more than 140 years ear­lier, al­ready strongly hinted at a pre­pon­der­ance of right-handed climbers; of the 40 species he stud­ied, 27 were right-handed and 13 left­handed (if the ap­pro­pri­ate sta­tis­ti­cal test had been in­vented at the time, this dif­fer­ence would have proved to be sig­nif­i­cant: i.e. the pro­por­tions of left and right-handed twin­ers was not ran­dom).

In fact, Dar­win seems to sug­gest that this was old news even then: “A greater num­ber of twin­ers re­volve in a course op­posed to that of the sun, or to the hands of a watch, than in the re­versed course, and, con­se­quently, the ma­jor­ity as­cend their sup­ports from left to right”.

Cu­ri­ously, Dar­win noted “I have seen no in­stance of two species of the same genus twin­ing in op­po­site direc­tions, and such cases must be rare”. One of the species he de­scribes is Wis­te­ria sinen­sis, which he cor­rectly notes is right-handed. The Chi­nese wis­te­ria was in­tro­duced to Bri­tain in 1816, and by 1835 was widely avail­able, so it’s not sur­pris­ing that Dar­win knew it. Down House, Dar­win’s home in Kent, is to­day home to a large Chi­nese wis­te­ria, and the ro­man­tic in me would like to be­lieve that it was planted by Dar­win him­self.

Although wa­ter­colours and black and white pho­tographs show Down House cov­ered by climbers, these are all long gone. A pho­to­graph from 1994 shows Down House com­pletely de­void of climbers, so its present cov­er­ing must all date from its ac­qui­si­tion in 1996 by English Her­itage, and it may just be an ac­ci­dent that the wis­te­ria is the “right” one.

It’s a pity that Dar­win was writ­ing just too soon to be aware of the Ja­panese wis­te­ria, Wis­te­ria flori­bunda, which wasn’t in­tro­duced from Ja­pan (via Hol­land) un­til the 1870s, so he was un­aware of its left-handed twin­ing (which thus al­lows it to be sep­a­rated from its Chi­nese cousin, even when com­pletely leaf­less).

Un­doubt­edly, how­ever, Dar­win was right that two species in the same genus twin­ing in op­po­site direc­tions must be rare; I don’t know of any apart from wis­te­ria. Col­lec­tors of botan­i­cal trivia will be de­lighted to learn that any hy­brid of Ja­panese wis­te­ria in­her­its its twin­ing di­rec­tion from that par­ent.

READER OF­FER From Dar­win’s Most Won­der­ful Plants: Dar­win’s Botany To­day by Ken Thomp­son (Pro­file Books, £10.99). Or­der yours now for £9.99 at books. tele­graph.co.uk

TWIRLING Wis­te­ria flori­bunda ‘Domino’, main; a wis­te­ria vine, right; and Ipo­moea tri­color ‘Heav­enlyBlue’, below

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