|Geranium robertianum, with a sprig of trailing blackberry leaves.|
Herb Robert. Also known as Stinky Bob, Red Robin, Death comes quickly, Storksbill, Dove's Foot, Crow's Foot, Dragonsblood, Bloodwort. And also, by gardeners, "That horrible weed." It grows anywhere, rapidly, and re-seeds itself enthusiastically, crowding out or completely smothering everything else. Luckily, the roots are shallow, and it is easily torn up. It always comes back, though.
Before I found its "real" name, I used to call it Stinky Geranium. It is one of the geraniums, and it does have a pungent odour, especially noticeable when you're ripping out armloads from your tidy landscaping.
The flowers are small, but their pink colour has a special carrying quality, so that they can be seen from a distance, even in shadowy undergrowth. The leaves turn red in dry conditions; on a wet bank, or in your lettuce plot, they're all green.
I wonder, though, where it got the name, "Death comes quickly." Nothing kills it.