What’s the point of the cactus?
‘It seemeth a strange herb,’ wrote the Spanish physician Nicolás Monardes in his Joyful News out of the New World (1568) of his first encounter with a cactus. ’One of its thorns pricked me. They are as sharp as needles and did hurt.’
Strange, certainly, and, in their serried ranks at the garden centre, unappealing – bulbous, warty and bristling, like a legion of warlike goblins. Or so they had always seemed until, last year, I visited the Huntington Desert Garden in southern California.
Henry Huntington founded the Pacific Electric Railway in 1901. Based initially in downtown Los Angeles, it grew within a few years into a mass-transit system of electrically operated street cars, linking the sprawling metropolis from north (Pasadena) to south (Long Beach), west (Beverly Hills) to east (Rialto). His foresight in buying large tracts of real estate alongside the routes of his streetcars made him the largest single landowner in California.
He was fantastically rich and, with his estimated fortune of 50 billion dollars, built an art gallery to house his collection of prints and paintings (Dürer, Rembrandt, Goya and Gainsborough) and a library to display his first editions of Shakespeare, the Gutenberg Bible, Chaucer’s Canterbury Tales and eight copies of Newton’s Principia Mathematica, two annotated by the author.
And he created the most extraordinary garden in the world, spread over ten acres of gently sloping, west-facing hillside below his palatial mansion in Pasadena. Here, ably assisted by his foreman, German landscape gardener William Hertrich and dozens of labourers, he planted more than 5,000 species of trees and plants culled from the deserts of five continents.
The visual effect on a hot bright morning in early summer was surreal and stupendous. It was as if you had been
transported to an alien planet where the usual rules of form and structure no longer applied: spindly grey green columns of euphorbia shooting 40 feet straight up into the sky; vast rosettes of stout, spiky-leaved agave sprouting from the arid soil; clumps of dragon trees, their battered trunks encrusted with red sap.
Most impressive of all, unsurpassed in their variety of shape and size, are the cacti, armed to the teeth with their dangerously sharp, needle-like, hooked and barbed spines. In May and June, their intensely hued blossoms outshine those of any other plant, visible for miles to their potential pollinators, bees, bats and hummingbirds.
Their popular names convey something of that exuberant profusion of shape and colour: the ‘silver torch’, handsome and erect, cloaked in snow-white bristles; the ‘hedgehog’, low-growing and inconspicuous, almost obscured by a mass of brilliant pink flowers; the ‘bishop’s mitre’, flat and star-shaped like a biretta with a showy blue pompom at its centre; the ‘pincushion’, covered with spiralling rows of nipple-like nodules; the large, spherical ‘golden barrel’, with its dazzling, symmetrical, bright yellow spines; and, bizarre in the extreme, the ‘creeping devil’, whose prickly, python-shaped stems worm their way across the ground.
The fabulous aesthetic impact of this symphony of exotic forms and colours is inseparable from the physiological miracle they represent. Each part is adapted to maximise their chances of survival in the arid desert heat. Put simply, this accounts for three of the cacti’s most distinctive features. First, they have dispensed with leaves – conserving all the moisture that in temperate plants is transpired through the minuscule stomata (or mouths) on their undersurface. Next, the internal structure of the stem is modified to store both water and carbon dioxide, whose combination, in the process of photosynthesis, forms the tissues from which all plants are made.
As for that armature of spines, while usefully defending the succulent cactus from thirsty desert-foragers, they also capture and condense the fog rolling in from the Pacific as the hot desert air is cooled by the ocean. This was discovered quite recently by researchers at the Natural History Museum, who used time-lapse photography to demonstrate droplets of water moving rapidly down the spines’ narrow grooves before being absorbed directly into the stem. Some 5,000 miles away, on the Namibian coast, the desert beetle Stenocara gracilipes similarly refreshes itself, gathering on its outstretched wings fog droplets that roll down its back into its mouth.
The wonders of nature never cease.
‘Their intensely hued blossoms are visible for miles to bees, bats and hummingbirds’