IN 2014 THE JOURNAL Current Biology published an account of some newly discovered properties of the Patagonian vine Boquila trifoliolata. They are, to say the least, unusual and appear to violate most existing ideas about plant adaptation and communication. Boquila is a thin-stalked woody climber which can spiral from ground level to high canopy, and is endemic to the temperate forests of South America. Its basic foliage pattern is composed of groups of three roughly spear-shaped leaves. What is not supposed to be possible is that these leaves are able to mimic the colour, shape, size and orientation of those of its host trees.
Habitat mimicry isn’t unknown in the plant world. Lithops species make a good job of disguising themselves as stones in deserts where every item of moisture-bearing food is hunted out voraciously. Boquila’s mimicry is unique in that it isn’t confined to copying just its immediate environment, or the leaves of a single host species. Its leaves stay within the green-blue spectrum and keep their formation, but as the vine winds through the tree community over weeks and months, the leaves morph to resemble those of each new supporting species, even ones it may never have encountered before. In the space of a few yards the leaves of a single vine can be as smooth as an ivy’s, more rounded like box, then bluish and deeply veined, then yellow-green, serrated, oval ended … The Chilean researchers who discovered this mysterious legerdemain, Ernesto Gianoli and Fernando Carrasco-Urra, made a series of photographs of entwined trees, and had to insert arrows to point out which leaves belong to the vine and which to the host trees, so difficult are they to tell apart. They suggest that the purpose of what is essentially an indefinitely flexible and bespoke camouflage technique may be to lower predation by insects, the vine’s leaves becoming invisible against the hosts’. But they have no idea how the vine does its trick, except that, in being able to cope with unfamiliar situations, it is demonstrating the first principle of intelligence.
They float a few theories, that the vine’s leaves are sensitive to volatile chemicals emitted by the host, that they are somehow provoked into rapid mutation – ‘gene jumping’ – but neither seems plausible. Maybe there are photo-receptors in the undersides of the leaves that trigger the changes. Plants are rich in cells which are sensitive to light, and they may have been modified in this species to respond to colours and shapes nearby. The caterpillars of some moth species have photo-receptive cells on their stomachs which kindle changes in body colour to mimic the surfaces they’re crawling over. You need to find analogies in the animal world to get any kind of grasp on what is happening. Giant squid, for example, seem able to change their colour at will. But the perils of analogy are shown by Boquila’s unofficial popular name of ‘chameleon vine’. It’s a neat tag, but misleading. Real chameleons don’t, as is often assumed, change colour to match their surroundings. Their layers of skin are responsive to temperature and to their mood during courtship and displays of aggression, and are modulated by hormone-like chemicals. When they do appear to mimic their habitats it is pure coincidence. (Boquila has also been tagged the ‘STEALTH vine’, after the American spy plane, hinting at the kind of organisation which will be most interested once its transformative mechanism has been unravelled.)
Meanwhile the vine is redolent with biological mystery and possibility. The gap between Boquila’s leaves and its hosts’ is a literal space, where unknown transactions of light and volatile chemicals and vaporous genes may be in progress. It’s also a metaphorical space, containing our existential distance from the plant world and its communication systems. It is hard for us to grasp that there are, for instance, ‘scents’ that we can’t smell, but which plants, noseless and brainless, can. What follows is an account of the growing understanding of plant senses, and what this might say about their status as intelligent organisms.