Although Maclean's Magazine recently called it "The Plant That's Eating B.C.," something Lower Mainlanders from Langley to Squamish would heartily endorse, Japanese knotweed's accomplishments far exceed such humble appellations: it's actually eating the world. Although the Sea to Sky Invasive Species Council has done a yeoman's job of keeping it out of Whistler, other places haven't been as lucky. In four decades of essays and scientific papers, botanist John Bailey has tracked the story of knotweed's migration from the Orient to his native Britain, where its human shepherds lost control and the plant became the greatest natural disaster that country has ever seen. The tale is instructive on many levels, but one particular facet seems responsible for the thoroughness with which knotweed blanketed its new home: no one saw it coming.
Until its forced relocation to Europe, Fallopia japonica var. japonica was a towering herbaceous perennial minding its own business in Japan, China and Korea, eking out a living as part of a giant herb community along riverbanks and forest edges. Here, natural checks and balances included competing for space and light with other plants, and struggling with a cadre of allelopathic neighbours (Allelopathy refers to the beneficial or harmful effects of one plant on another plant), rapacious invertebrates, and pathogenic fungi. Once freed of such constraints, however, this hollow-stalked, luxuriously leafed, and pleasingly florescent "false bamboo" grew with startling vigour under a range of conditions. It was thus presented as a handsome — and salable — garden ornamental to the colourful Dutch surgeon and explorer Phillip von Siebold by his Japanese hosts while he was stationed there from 1823 to 1829. Most of his collection of live plants, including knotweed, made it back to Holland, but a series of "fascinating peregrinations" that included shipwreck, imprisonment and civil war kept Siebold from reuniting with them until 1841.
Having fared better than he over the period, the knotweed was soon flourishing in a "Garden of Accilimatisation" set up in Leiden to feed sales of a new horticultural venture, Von Siebold & Company, winning a gold medal from the Society of Agriculture & Horticulture at Utrecht in 1847 for Most Interesting New Ornamental Plant. Subsequent Von Siebold & Co. catalogue descriptions built on this accolade while also ascribing an eyebrow-raising litany of medicinal and practical properties, the only free of hyperbole being a claim that knotweed was "inextirpable." Propelled by salesmanship, knotweed began its march across the continent, laying siege to castles and communes, gardens and ghettos. It would eventually sail onward to the foreign holdings of most European countries as nursery stock — plus vegetative bits concealed in the soil used as ballast at the time, soil dumped at the other end to make way for cargo.
Plant cultivation was hot in Victorian times, and the insatiable demand for unique forms at first saw giddy gardeners snapping up Siebold's knotweed — despite a premium price (anything that grew this easily was expensive, because customers wouldn't return). Overlooked in the rumpus, however, were the habits and habitus of a bonsai version of the plant, Fallopia japonica var. compacta, whose early colonization and often sole-occupancy of lava fields on Japanese volcanoes spoke volumes about the species' capabilities. Knotweed's subsequent proficiency as an invader, in fact, points to one such facilitative evolutionary adaptation: the ability to survive coatings of hot volcanic ash by storing enormous amounts of energy in an extensive woody rhizome that could reach depths of three metres and travel five times that horizontally — a veritable underground tree. Thus engendered, the rhizome, or parts thereof as small as a fingernail, could remain dormant up to a decade only to bud at a moment's exposure to air or water in a shifting substrate. Although this seemingly miraculous regeneration lies at the root (sorry) of knotweed's spread, also worth noting are its hydraulic abilities: thick, blunt shoots and rapid rhizome expansion could crack and split difficult substrates like lava, but also concrete, asphalt or masonry, making it further problematic around dwellings and other infrastructure.
Sure enough, Bailey and fellow botanist Ann Connolly would trace Britain's first critical knotweed introduction to a single male-sterile plant (female clone) donated by "a certain Mr. Siebold of Leyden on 9 August 1850" to the Royal Botanical Gardens at Kew, where it appears as Item 34 on a manifest of Asiatic plants Siebold doubtless hoped would curry favour for the exchange of other novelties. Passed from public gardens to commercial nurseries to private and estate gardens, the popular ornamental thrived in a sooty, sulfurous, mid-19th century city environment where other exotics flagged. By the turn of the century, however, knotweed had escaped all but the most rigorous of confines in numerous locales. Some of the earliest non-garden records would come from the volcano-like spoil heaps of Welsh coal mines, though it remains unknown whether this was adventitious or deliberate — possibly planted to help stabilize friable slopes. Though few corners of the British Isles are these days free of knotweed, Wales remains an epicentre of infestation.
By the time the plant's true nature was apparent, it was too late, and attempts to dispose of it only caused further spread: cutting it back could result in as many new plants as there were pieces, as well as redoubled growth from the rhizomes; digging it up and moving the soil was equally facilitative, seeing not only vigorous re-growth at disposal sites, but from overlooked fragments in the dig. It was like trying to put out a fire by spreading its smoldering embers far and wide with a shovel, then adding more fuel to the original conflagration. Watercourses proved particularly vulnerable; pulling a chair up to the water table with no suitable competitors in sight, knotweed took off, shading out all native vegetation while its prying rhizomes fissured even the most solid riparian areas, tumbling itself into floodwaters to effectively spread downstream (something I've observed firsthand in Squamish). By the late 1970s, knotweed's U.K. conquest not only had scientists' attention (Connolly's 1977 opus on the true extent of the infestation was groundbreaking — pun intended), but also the gentry clamouring for action. The government's first overture was the 1981 Wildlife and Countryside Act, which criminalized the planting of Japanese knotweed or otherwise nurturing its growth in the wild. The plant, however, never got the memo, continuing its spread unabated — and not just because of toothless, difficult-to-enforce legislation that also failed to explicitly prohibit transport of contaminated soil. As would soon be discovered, more insidious forces were at work...
Next week: Knot in my backyard Part II: swarming
Leslie Anthony is a Whistler-based author, editor, biologist and bon vivant who has never met a mountain he didn't like.