Koenigia alaskana

Koenigia alaskana (synonym Aconogonon alaskanum, Persicaria alpina) is an Asian and North American species of flowering plant in the buckwheat family known by the common names Alaska wild-rhubarb and alpine knotweed. 
Description.
This herbaceous perennial grows up to 2 meters (almost 7 feet) tall, with a woody root. Flowers are white or pale green, borne in elongated arrays.
Distribution.
"Koenigia alaskana" is native to Alaska, the Yukon, and Magadan Oblast in the Russian Far East.
Cultivation.
It is cultivated in areas with enough space for its substantial mounds of foliage. Under the name "Persicaria alpina" it has received the Royal Horticultural Society's Award of Garden Merit. 