Japanese Knotweed Morphology

(Fallopia japonica)

Picturesque scene of Japanese Knotweed monoculture growing along a mountain stream in Bohemia (Czech Republic)Japanese Knotweed is a tall herbaceous plant (dies down in winter) perennial (lives for ever!) with an extensive underground woody rhizome system, which is responsible for its spread and A RAPD gel of a selection of Japanese Knotweed colonies from around Britain showing no genetic differencespersistence. In the Autumn it has masses of small white flowers that are attractive to bees wasps and flies.  In a number of In appropriate conditions huge amounts of viable seed may be found on Japanese Knotweed plants in Britain, this example is from Dolgellau, Walessenses it is an extraordinary plant.  Its vigorous powers of vegetative reproduction mean that it has been able to spread to all parts of the British Isles without the aid of sexual reproduction.  In Britain it is in fact a single female clone, and although the same clone also occurs in Europe and America, it is possible that additional clones exist  there. (Hollingsworth & Bailey 2000). Since only female plants occur in Britain they are unable to reproduce sexually, but are available for pollination by any related species in the area.  This they do very well, and most seed collected from F. japonica in Britain is the result of pollination by the related Russian Vine (Fallopia baldschuanica), to give Fallopia x conollyana. In locations where Japanese Knotweed grows close to male plants of Giant Knotweed or the hybrid F. x bohemica, enormous amounts of seed can be produced some years. This seed germinates readily in greenhouse conditions to produce vigorous young plants.

Conolly paper (1977) 

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