I think knotweeds are charming and an exciting challenge to observe and identify. I’m not satisfied with just leaving them at P. aviculare. Normally the value of ID’ing to subspecies is debatable, but this dissatisfaction has resulted in me learning that many of what FNA and some other florae treat as subspecies of P. aviculare, other florae (and POWO) treat as distinct species. So if one keys something to P. aviculare and stops there, without getting down to subspecies, they’re quite likely to be misidentifying the plant in question!
What do you think about knotweeds? Are they worth your time?