Persicaria maculosa

Lady's-thumb, Redshank, Spotted lady's-thumb , Smart weed; 

Persicaria maculosa
(syn. Polygonum persicaria) is an annual plant in the knotweed family, Polygonaceae. Common names include lady's thumb,[1] spotted lady's thumb, Jesusplant, and redshank.[2]
It is native to Eurasia and present as an introduced and invasive species in North America, where it was first noted in the Great Lakes region in 1843.[3]
Redshank is an annual herb with an erect rather floppy stem with swollen joints, growing to a height of 10 to 60 cm (4 to 24 in). The leaves are alternate and almost stalkless. The leaf blades often have a brown or black spot in the centre and are narrowly ovate and have entire margins. Each leaf base has stipules which are fused into a stem-enclosing sheath that is loose and fringed with long hairs at the upper end. The inflorescence is a dense spike. The perianth of each tiny pink flower consists of four or five lobes, fused near the base. There are six stamens, two fused carpels and two styles. The fruit is a shiny black, three-edged achene. This plant flowers from July to September.[4]
It is native to Europe and Asia, where it can be mistaken for Polygonum minus. The latter has narrower leaves, usually less than 1 cm wide. It has been introduced to North America and is naturalised throughout the mainland continent,[5] growing along roadsides, riverbanks, and on fallow ground. In the USA, it is very similar to Pennsylvania smartweed, but redshank has a fringe of hairs at the top of the ochrea, something which Pennsylvania smartweed lacks.
This plant contains persicarin and tannins. In medicine, Redshank is used against diarrhoea and infections. The leaves and young shoots may be eaten as a palatable and nutritious leaf vegetable. It is often seen as a weed and rarely cultivated. A yellow dye can be produced from this plant with alum used as a mordant.
(From  Wikipedia on 8.1.14)
Polygonum for id 150211MK1: Please help to is this Polygonaceae member. I hope the genus is Polygonum sp. I found this single individual in a first-order stream among P.glabrum population. The location is on the eastern most part of Nilgiris district in TN.
Date/Time- 10-02-2011 / 11:00 AM
Location- Place, Altitude, GP stream in Nilgiris RF; TN. c 350 msl
Habitat- Garden/ Urban/ Wild/ Type- wild, wetland
Plant Habit-herb
Height/Length- c. 50 cm
Leaves Type/ Shape/ Size- c. 10 X 1 cm; Violet blotches in mid of leaf
Inflorescence Type/ Size- raceme; upto 10cm long
Flowers Size/ Colour/ Calyx/ Bracts- white

Germanname Knöterich. But I have this weed in my garden in Ritterhude, not just white but redisch too. I don't think I have a foto of the red one. Will send some in summer.
Sending Knöterich from my garden in a new mail.
seems to be Polygonum barbatum 
Leaves with dark blotches in middle, spikes dense and compact. Persicaria maculosa from me.
Thank you .. for the identification. Polygonum barbatum have ciliated ochre