giant mountain fleece flower edible ?

Does any one know if giant mountain fleece flower persicaria polymorpha (also known as polygonum polymorphum)  is edible ?

http://plants.for9.net/edible-and-medicinal-plants/polygonum-polymorphum/

This is the closest I could see to it being recommended.  It is also known as knotweed and is closely related to other knotweeds that are edible.  

Doing a search for poisonous knot weed, I just find the oxalic acid concerns and that consuming very large quantities can lead to a person becoming very sensitive to the sun.

I might be willing to try a very small amount treated like Japanese knotweed,  but I wouldn't be willing to test it on my nieces. Definitely a case of proceed with caution.