Does anybody recognize this description? This perennial plant has red roots that spread, they are about 1/4 inch thick and break easily. The stems are about 12-18 inches high, with a lavender flower cluster at the top in late summer or early autum. The lower part of the mature stem turns red. The leaves come off the stem in alternate pairs about every inch, and are 1 1/2 inch long with 3 prominent veins running the length of the leaf. The leaves come out of a little band that circles the stem. There are no branches but a root will often put up several stems. It is very xeric, hardy in zone 5, and needs no encouragement to grow, definitely invasive. I checked the plant database. Somebody somewhere knows what this is.
SOLVED: invasive pest plant
I'm being old fashoined Polygonum is now in the Persicaria genus (silly Baa!)
Thanks Baa, I looked at the link you gave and can't really tell. I couldn't see enough of the leaves in the picture of the Bisort becasue of the grass. Also the blooms on mine do not stand up so high. The color is right though.
Zany, I looked at your link, it's not the same plant. Mine is taller and not reddish except for the lower part of the mature stems, also not a round blossom cluster. Thanks for trying.
Sorry Mary I should be more clear :) The page on the hyperlink is a number of species in the Persicaria genus as your species might be particular to your region. Your description reminded me of the Persicaria (was Polygonum) genus but I daren't hazzard a guess to species.
Right Baa, it could be a near relative of P. Bisort, maybe some thing that has changed a little over the years. I didn't see a description with that picture. Maybe should look again, I might have missed it.