Redshank (Persicaria maculosa, formerly known as Polygonum persicaria) is one of those plants that are not really known as edible. It's a rather common weed though, native to Europe and an invasive species in the US, but redshank seems to grow so modestly that no one seems to notice it . But take a look at this close-up of the flower. How pretty is that?
Very typical for wild edible plant is the black dot on the leaf, hence it's common name spotted lady's thumb. Other folk names include persicaria, redleg, lady's-thumb, gambetta, and Adam's plaster.
The leaves and young shoots can be eaten as a palatable and nutritious leafy green. Their taste is rather bland. In fact, redshank doesn't even taste "green", which is an advantage if you want to add greens to your diet but are a bit weary of their taste. As the plant grows taller and starts to flower, the leaf gets tougher, but not too tough to chew on (though this is a very personal thing of course).
In this case, the absense of flavor by no means indicates lack of nutrients! So add redshank to your juices, dips, soups as a free green superfood and enjoy.
And later on, the seed can be collected, but it is rather small and fiddly to use.