Of interest this week at Beal...

Japanese knotweed Polygonum cuspidatum Family: the Buckwheat family, the Polygonaceae Also called: Mexican bamboo, sacred bamboo, W. J. Beal mile-a-minute plant, Japanese fleece flower, or reynoutria Botanical Garden Japanese knotweed, Polygonum cuspidatum, has been in the United States since before 1890. It was probably imported as an ornamental garden accent plant, a role it still occasionally claims today. The common names Mexican bamboo, sacred bamboo, and Japanese fleece flower, probably all originate from that heritage. Although revered for its flowers and occasionally used as a food plant, its is most important for being one of the most aggressive and exclusionary invasive weeds ever established.

Polygonum cuspidatum, sometimes referred to the genus Fallopia, is a perennial herbaceous plant, often mistaken for a woody shrub, that is from 4 to 10 feet in height and establishes a colonial habit by way of its fast-spreading rhizome. The common name ‘mile-a-minute plant’ is in tribute to this characteristic. Its colonies, that can each exceed 3 acres in size, are so dense that virtually no other plant life can penetrate its crowded shade.

Japanese knotweed is native to Japan, Korea, Taiwan and China, but its has become a pest plant in most of temperate Asia, Russia, Europe, Britain, as well as the United States and Canada. We are fortunate in Michigan because in most years the growing season is not sufficient to ripen a large crop of seed. One look at California, Oregon, and Washington states shows that thousands of acres can be lost to this invader.

Japanese knotweed is not without uses however. The newly emerged spring shoots (above line of photos, second from the right) once stripped of their leaves, can be boiled and used as a substitute for rhubarb in deserts and pastries. Like rhubarb they derive their tangy flavoring from oxalic acid and therefore should be eaten in moderation. The subterranean rhizomes once excavated, can be boiled and sliced as a wilted salad ingredient. Large dead over-wintering stalks have been used for the construction of homemade flutes. With the extremely rapid growth rate and tall stature, Japanese knotweed has been used as a vegetative screen to hide dumps and waste places. The spikes of the white flowers ofPolygonum cuspidatum are usually dioecious (male or female). They clearly display the mem- branous ochrea, a sheath from which buds and shoots emerge, that are the hallmark of flower and leaf nodes in this family.

ochrea

Besides typical Polygonum cuspidatum, its ally giant knotweed, Polygonum sachalinense, with heart-shaped leaves to 1 foot in length, and stalks reaching in excess of 12 feet in height, has also been introduced to North America. As its name implies, it is native to the Sakhalin Islands, territory contested between Japan and Russia. The hybrid created by interbreeding between these two species is called Bohemian knotweed (P. x bohemica), but this complex is still often called Japanese knotweed.