This grower is sure of this plant identification.
Persicaria bistora ‘Superba’ (Polygonum). This is a genus of about 70 species of annuals and perennials and also some sub-shrubs. They may be evergreen, semi-evergreen or deciduous. They have spikes or panicles of small, usually long-lasting funnel, bell or cup-shaped flowers, which are followed by brown-red 3-angled or ovoid fruits. The genus Polygonum is often used to classify the species in this genus.