Polygonum sp. 'Sao Paulo' is another name for Persicaria sp. 'Sao Paulo', a knotweed that turns reddish under water; the two genera were long regarded as one but are now kept separate.12 It probably comes from Brazil, from São Paulo or its surroundings.2 Its species has not been conclusively resolved: P. hydropiperoides had been suspected, whereas an identification presented in 2024 points to P. punctata, whose sepals are entirely covered in glandular dots.34
It grows strictly upright with rather lanceolate leaves, the youngest of which bend downwards; in good light the foliage turns an intense magenta along almost the entire shoot.23 Strong light, CO₂ supplementation and plenty of iron and phosphate are recommended; a few stems in a small group are enough for an accent of colour.23 The bushier 'Kawagoeanum', coloured more pink to orange, is often sold under its name.23
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