Most of us go up and down steps and slopes without stopping to think about it, unless an injury or advancing age turns it into a conscious effort. Some of us enjoy the physical challenges and rewards of hill walking. A few serious
mountaineers get kicks out of trying to get up sheer rock faces.
As usual, plants got there ahead of us. Competition for light, space and the attentions of pollinating insects produces a range of different strategies and ingenious bits of bio-engineering. Some plants get their advantage from central strength. Tree trunks are a magnificent example of strength – and the fall of a mature tree in a gale is an awesome example of catastrophic failure. Short-lived annual plants, and perennials that die back in winter, have to work a lot faster and need different tactics.
The simplest method is just to sprawl over a stronger neighbouring plant. Hedge Bedstraw, for example, has very light stems, but can get its small leaves and tiny frothy-looking flowers to heights of a metre or more simply by lying against something else. Closely related Goosegrass aka Cleavers probably uses the tiny hooks on its leaves and stems to get a bit more purchase on its support. Brambles and Roses invest energy into producing large and distinctly vicious thorns. They are perfectly capable of taking care of themselves as free-standing shrubs, in which case the thorns must be more of a defence mechanism than a set of built-in crampons, but young plants may well use them to scramble and prop themselves up until their stems are strong enough to be independent.
An apparently straightforward, no-nonsense approach to gaining height is to have a flexible stem that can twine. You just wave about till you find a suitable climbing frame, then wind round and up it like a spiral staircase. Here’s a video of a Hop, Humulus lupulus, going up the pole. (Sorry, but you’ll need to watch or skip an ad before you get to it!). Bindweeds and Honeysuckle are the best examples of twining plants at St Nicks. Most of us have always believed (like the Flanders and Swan song, and a Wildwatch member who regularly sings it), that Bindweed goes
anti-clockwise while Honeysuckle goes clockwise. It seems that it’s not quite so simple. All plants can move to some extent. Stems grow, leaf and flower buds open and adjust for optimum conditions, roots seek out nutrients. But that’s not all. Darwin seems to have been among the first to describe a process called circumnutation (long word that means “nodding around”), in which plant parts trace an ellipse or helix as they grow. Research is still going on into how and why it happens. They’ve even taken sunflower seedlings on space flights to see if they still circumnutate without gravity and sunlight. Apparently most but not all of them do. The ability to twine seems to be a more specialised development of circumnutation, and it looks as if yes, it’s true that a particular species tends to go in a particular direction, but it can go in the opposite direction if it has to.
Other climbing plants use tendrils. Their main stems don’t twine, but they use specialised twining extensions of stems and leaves to hang on with. Human-invented wire plant ties are a very clunky equivalent. At St Nicks the place to look for tendrils is among members of the legume family – and if you’re interested in legumes, you do need to look for tendrils because they can be a useful identification feature. Clover and Bird’s-foot Trefoil don’t bother with them. They like open ground with low-growing vegetation where they can spread sideways. Ribbed Melilot and Goat’s Rue form small bushes that don’t need extra support. Meadow Vetchling has single or simply branched tendrils emerging
from between its paired leaflets; Common Vetch, Bush Vetch and Tufted Vetch produce multiple-branched tendrils from the tips of compound leaflets. They all use them to wind around neighbouring plants to gain additional support for relatively weak stems.
If you want to see tendril technology developed into interactive cable-coiling, look for White Bryony. The only native member of the Cucumber family, this very attractive plant puts out a long tendril, finds a suitable support, winds firmly round it, then coils the tendril tightly to haul itself into place. As evidence of ability to change direction, the coils sometimes kink like the hand set cable of your land-line or shaver flex. Wildwatch members have sometimes wondered how long you’d need to stand with your finger against a Bryony tendril before it started to wind you in. So far nobody’s actually tried it.
Ivy is an evergreen plant, so it’s probably not a coincidence that in plant terms it puts even more effort into climbing. It’s at the serious mountaineering end of the business. Gardeners find Ivy useful because it doesn’t mind growing in shade – but it needs sunlight to stimulate flowering, so it has developed yet another technique to be able to climb to up to it. It can scale any natural hard surface or man-made bricks and concrete, using aerial “rootlets”. Current research suggests that these rootlets cling by producing an adhesive substance rather than by digging into the surface, and that they have little or no part in nourishing the plant. If it finds a promising crack in the surface, Ivy might seize the opportunity to put a proper root into it, and if its main stem is damaged it will do its best to re-root higher up, but evidence suggests that the rootlets for climbing don’t damage sound surfaces. If you have worries about Ivy on a house or garden wall, try the first link below, which reports a research seminar set up by English Heritage and Oxford University, with the National Trust contributing advice on how best to get it off structures where you don’t want it.
So – next time you’re out for a walk, whether it’s in the countryside or a park or garden, look out for other species that use these methods, and sooner or later you’ll spot a plant that does it a bit differently.
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