If we are to ever find out how these plants are spreading, and hybridising it is very important to be able to identify them correctly.  F. x bohemica is the most difficult to identify, as specimens with large leaves get lumped with F. sachalinensis and those with smaller leaves can be confused with F. japonica.  Although there are good chromosomal differences, in practical terms the best characters to use are leaf shape and size and the trichomes (hairs) of the lower epidermis (underside) of the leaf. One should always use the largest available leaf, and ensure that it is a fully grown example - early season growth is not so good.  Using the figure and the trichome photographs it can be seen that F. japonica has small hairless leaves with truncte leaf bases, F. sachalinensis has much larger leaves with scattered long hairs on the lower epidermis, and with a very cordate (Heart shaped) leaf base.  The hybrid (F. x bohemica) has leaves of intermediate shape and size, which can on occasion be very difficult to distinguish from F. sachalinensis.  In order to overcome this problem we need to look at the trichomes (hairs) along the veins of the lower epidermis of the leaf.  The photographs show that in F. japonica we only have heavily striated bumps that one wouldn't normally term trichomes. F. sachalinensis at the other extreme has with very long (sometimes as many as 14 cells) thin walled hairs, without any striations which readily collapse when dried.  The important feature is that the hybrid plants have hairs that are in every way intermediate between F. japonica and F. sachalinensis, and are hence of great taxonomic value.  These hybrid hairs are much shorter, thicker and more striate than the F. sachalinensis ones, are are a clear indication of hybridity.  These characters are easily preserved by drying the leaves as quickly as possible in a flat position - a telephone directory or pile of newspaper, with a weight on will suffice if you do not have a herbarium press.  The secret is to keep changing the drying paper every day.   

Leaf characters are very useful for distinguishing these four taxa - epidermal  characters are also very important


F. japonica var . japonica doesn’t  really have hairs on its leaves, just heavily ornamented single cells F. x bohemica has hairs on the underside of its leaf that are intermediate in length and degree of ornamentation

The epidermal hairs of F. sachalinensis have long thin-walled cells that often collapse on dried specimens 

Fallopia x conollyana is characterised by its smaller more triangular leaves with cordate bases, the flowers when produced are more diagnostic.

Bailey & Conolly (1991) 

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