TECHNICAL BULLETIN
ISSUE 29
JULY 2018
JAPANESE KNOTWEED – UNDERSTANDING THE PLANT DR DAN JONES SUMMARISES THE RESEARCH CONDUCTED BY SWANSEA UNIVERSITY DR DAN JONES PHD, MSC, BSC, GCIEEM
MANAGING DIRECTOR, ADVANCED INVASIVES LTD
Fall from grace
Japanese knotweed (Fallopia japonica var. japonica), is one of a number of knotweed species, introduced into Europe in the mid-19th century (1841) by Philipp Franz Balthasar von Siebold, a German botanist and physician living in The Netherlands. In 1850 he sent a specimen of Japanese knotweed to Kew Gardens in London. Kew offered the plant for sale to local commercial nurseries, and by 1854, knotweed had travelled as far as the Royal Botanical Gardens in Edinburgh. Since first escaping from cultivation in Maesteg, Wales in 1886, Japanese knotweed now has a well-established range across the UK. It is found in over 70% of the UK hectads – 10km×10km grid-squares that are used to see how widely distributed plants and animals are. It is worth noting that although knotweed may be present in these hectads, it is not necessarily abundant throughout each grid. Further afield, knotweed is now established across mainland Europe, North America and the Southern Hemisphere. This global spread is astonishing; particularly, as to date, this has mainly occurred via plant fragments (vegetative) and not from (viable) seed.
Figure 1: Japanese knotweed in flower, Cardiff. © Advanced Invasives 2018
to 2.5m tall and it is visually striking – particularly in the summer and autumn months when it produces abundant creamy-white blossoms. However, as an ecologist, plant ‘traits’ such as ease of propagation and spread are precisely why knotweed has, and will continue to be, quite literally a huge problem; both for native biodiversity and increasingly, wider society.
From a horticultural perspective it is clear why knotweed was so prized for planting schemes: it is easy to propagate (spread), growing rapidly from early in the growing season
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