Persicaria sp. 'Kawagoeanum'

Persicaria (or Polygonum) sp. 'Kawagoeanum' (sometimes also called Polygonum sp. 'Pink') is a relatively new aquarium plant. It is still not quite clear which species it belongs to, it could be Persicaria kawagoeana (= Polygonum kawagoeanum) from East Asia, though. Like most knotweeds, it inhabits wet locations like bogs, ditches or riverbanks. It grows above as well as below the waterline.
Accordingly, Persicaria sp. 'Kawagoeanum' can be cultivated emersed as well as submersed. It is not regularly found in pet stores or online shops, and is usually more readily available from other hobbyists.

P. sp. 'Kawagoeanum' is often mistaken for Persicaria (Polygonum) sp. 'Sao Paulo', and it has been in trade under that erroneous name, too.
For differentiation, please see the description of Persicaria sp. 'Sao Paulo'.

The cultivation of P. sp. 'Kawagoeanum' is not especially difficult if its basic requirements are met. It may not be a suitable plant for low-tech aquaria, however, it is still useful for most aquarists. Strong light from metal halide lamps, compact or T5 lamps is recommendable, as this plant will only then develop a highly intensive pink-orange colour. Strong light will also reduce its (totally normal) tendency to lose its lowermost leaves.

High levels of CO2, phosphate and iron as well as a light colour temperature of 6500 to 8000 Kelvin also contribute to an intensive colour.
Furthermore, this plant does not tend to have growth problems. Emersed cultivation will lead to a significantly increased growth rate even though it may not grow under optimal conditions. Under intensive artificial light or under sunlight, the leaves will develop a rather attractive V-shaped brown spot on their upper side (comparable to spotted lady's thumb, a plant frequently found in Europe).

In contrast to other knotweed species used as aquarium plants, the growth habit of P. sp. 'Kawagoeanum' is not strictly upright. Instead, it ramifies at short intervals and thus forms a dense, easy-to-maintain bush. This makes it a better plant for Japanese-style Nature Aquarium layouts than for carefully trimmed Dutch tanks.
Considering its tendency to lose its lowermost leaves, it makes a lot of sense to hide these parts of the stems with driftwood or middleground plants.
The optics of P. sp. 'Kawagoeanum' and Cyperus helferi ideally complement each other, and both are great background plants for medium and large aquaria.