While collecting, I saw loads of these things,
It's Alliaria petiolata, or wild "garlic mustard" (sometimes Sisymbrium alliaria, "Hedge-Garlic," "Sauce-Alone," "Jack-by-the-Hedge," "Poor Man's Mustard," "Garlicwort," "Mustard Root"...) a plant that is another of these super-greens, chock full of vitamins C and A. Nice peppery slightly garlicky taste. Good cooked or fresh. The roots make an excellent horseradish.
It's also very common in North American fields too, brought over by settlers for whom it was a standard vegetable. They soon escaped the gardens and went wild.
Wiki says, "Garlic mustard is one of the oldest discovered spices to be used in cooking in Europe. Evidence of its use has been found from archeological remains found in the Baltic, dating back to 6100-5750...In 17th century Britain it was recommended as a flavouring for salt fish. It can also be made into a sauce for eating with roast lamb or salad."
It grows abundantly in the same kind of conditions as nettles, and so they are often side by side. They also look quite similar at first glance, with their heart shaped toothed leaves. But the flowers are totally different, and come out much earlier than nettle flowers. Nettles aren't as nice once they've started flowering and I would only collect them for drying at that point. But the garlic mustard is lovely even in the midst of its flowering time, which happens to be right now.
It was valued by Oldfangled people across Europe for medicinal applications. It has excellent antiseptic properties and can be applied to cuts to prevent infection. That garlicky flavor comes from sulfur, which is one of the best natural anti-microbials. But the sulphur is lost when it is heated, so the antiseptic properties can be gained only with cold-processing. Cooking makes the plant taste milder for that reason.
The Modern Herbal webpage says the juice of the leaves is a "deobstruent," which can be added to honey (though I think that would taste a bit strange) is useful for treating dropsy. Dropsy is a quaint term for oedema, which I started to experience rather badly last summer. It's a common long-term side effect of the surgery I had, having a bunch of lymph nodes removed. I'm constantly in search of things that will help, so maybe I'll try making a tincture or something.
The roots can be added to fire water or fire vinegar as it is often called. This is a simple and well used tincture where garlic, onions, grated ginger, horseradish, and hot peppers are covered with apple cider vinegar and let sit for several months. Adding garlic mustard root just gives it that much more of a kick. Take a couple tablespoons of this in 8 ounces of water at the first sign of a cold. It will either knock that cold right out or shorten it considerably. People use fire water for so many different ailments it warrants a post all its own.
Even a garlic mustard root/apple cider vinegar tincture on its own will help with bacterial and viral infections. A steam of the leaves and roots can help loosen chest and sinus infections as well as warm up people who have a chill from being out in the cold too long without the proper gear.
As a member of the Brassica family, it's related to broccoli, cabbage and sprouts, and is loaded with the same nutrient group you find in those. But as a wild plant, it is much more nutrient-dense.
Someone out there in Innernet Land suggested making a pesto out of the leaves. I might try it.