The distribution and origins of Fallopia x bohemica (Polygonaceae) in Europe

Fallopia x bohemica is a good example of a hybrid occurring when two introduced species come in contact in their adventive range. Although only recognised in the early 1980's, herbarium material and the current distribution pattern suggest that it has long been an unrecognised part of the Japanese Knotweed s.l. population. The identification, distribution, cytological background, history and some of the ecological determinants of the spread in Europe are provided along with a substantial citation of field observations and herbarium specimens used to produce the distribution map. This is the first attempt to map its European distribution, and must be regarded as provisional since comprehensive recording of its distribution is limited to a handful of countries. The unexpected discovery for the first time of this taxon in the Mediterranean is also reported. It is to be hoped that this paper will provide the impetus for a more comprehensive study of this invidious and under-recorded taxon.