A Persicaria spp. Can't name species without seeing fresh leaves.

No. Not bamboo. Some kind of Persicaria is a good call.

Cannot provide fresh leaves. This was the only piece -- it did not have a flower -- yet and since I pulled it no possibility to see if Persicaria is a match. But not bamboo most importantly. Thanks to all.

But not bamboo most importantly.

Not necessarily. 😁 The possibility of something far more sinister than bamboo exists and does have the ability to pop up spotaneously, which bamboo does not. I agree it is likely to be something in the Polygonaceae (Fallopia, Bistorta, Persicaria, Polygonum, Reynoutria, etc), but not clear enough to nail down a particular species. Besides, they seem to change names every few weeks anyway!!

At least your mystery plant does not appear to be one of the really bad guys of the family, Reynoutria or the giant knotweeds. Those are serious invaders and are far more difficult to control than any bamboo.

I cut a lot of flowers in my garden and then forget about them. This morning I looked at a snip from a couple of days ago and I do think it's from that mystery plant. I looked at pics of Persicaria and that is it. So, is that a decent plant? I rather like the little flower. Not a weed, eh? But if so, I really don't mind weeds if they have a nice flower..

I also like the flowers and I let vollunteer Persicaria grow when they show up. Most of the native and non native Persicaria species have similar leaves and flowers. The only exception would be Persicaria perfoliata, The Mile a Minute Vine. It's extremely agressive and behaves more like it's Falopia Climbing Buckwheat relatives. Some of the Persicaria species were supposed to be moved into the genus Anteneron. The problem with showy Persicaria cultivars of Eurasian species is the danger of them being introduced into our natural ecosystems. Persicaria pensylvanica is the most common species in my area. I really like the aquatic Persicaria amphibia as well.

I just want to clarify that there's only 1 species of Persicaria that has been considered to be placed into a seperate genus. It's Virginia Jumpseed aka Woodland Knotweed, Pericaria virginiana. Virginia Jumpseed has a long flower stem with the flowers seperately spaced out, while the other Persicaria,(Smartweeds) have a much shorter flower stems and the flowers are held together in s tight cluster. Persicaria virginiana has an Asian lookalike named Persicaria filiformis. Filiformis has red flowers and is sold in the trade. The danger is that it can be easily confused with our native jumpseed.

Virginia Jumpseed

Pennsylvania Smartweed

Virginia Jumpseed

Asian Jumpseed, Persicaria filiformis

Asian Jumpseed