This common plant is called by a number of names in addition to Spanish Needle - everything from "Hairy Beggarticks" (yuck!) to "Piquant Noir" (ooh la la!). Its scientific name is Bidens Pilosa, and I first knew it as simple "bidens" - although I've called it some unsavory names when it kept popping up in my butterfly/herb garden. It grows like a, ummm, weed, and its root system is a real booger if you don't pull it quick.
However... I learned recently that it's edible. Susan Marynowski, a local herbalist suggests throwing a handful of leaves into soups, stews, or greens to add nutrients. It has medicinal qualities as well; its leaves are chewed for sore throat or boiled to make a tea that is said to help with upper-respiratory infections.
It seems to thrive just about anyplace. Walking along the sidewalk off a very busy road, I found a long row of it growing happily in the cracks - and we have had exactly one rainy day during the last six weeks! It's advised that we don't eat wild edibles growing on the side of the road due to the street run-off, but if you look, you'll probably find it growing around your yard as I did. It's hardy, persistent, tolerant, and honestly - it's kind of pretty when it's blooming. Sometimes I try to think of these plants like folk herbalists used to - that hidden in their appearance or their character lies clue to how they might benefit us. Hardiness, persistence, tolerance, ability to bloom under difficult circumstances - all good human qualities. Plus I have a cold.