Someone was expressing fear of Russian Vine hybridising with Japanese
Knotweed.

It does.

Fide Stace, most seed produced by Fallopia japonica in the UK is hybrid,
with either Fallopia sakhalinensis or Fallopia baldschuanica as the
pollen parent.

(Fallopia japonica spreads vegetatively; most plants in the UK are
octoploid females, so in the absence of males hybrid seed is produced
instead.)

Although seed of Fallopia japonica x baldschuanica is viable only one
hybrid has been recorded in the wild.
--
Stewart Robert Hinsley