Compare your plant to Ornithogalum umbellatum, Star of Bethlehem. If so, then your instinct was right. It's a terribly invasive pest. Here is a link that might be useful: Google image results

This is a guess based in the winged stems. There is a plant called Wingstem, Verbesina species, which I have never seen. I am sure some of the US based folk can id it more precisely. Perhaps that is what you have there. The colour looks to me like a nutritional problem loosely called chlorosis. I don't think it would be a stable characteristic.

This one should work. Safe for floratam. Hose end sprayer. http://www.ortho.com/smg/goprod/ortho-weed-b-gon-weed-killer/prod11360002?locale=en_US More expensive that is also safe for floratam. Out of stock here but available elsewhere. http://www.domyownpestcontrol.com/celsius-wg-herbicide-p-1923.html Don't worry about the mediocre reviews for the Ortho product. Most folks don't bother to read the label and then misapply. I've used Weed B Gon products with great success. It's more about the ingredients than the brand and proper application.

Maybe because the stuff growing near our house in Parker smelled so good the flowers were picked often.....could be why it didn't spread much I guess, but I certainly wouldn't call what I saw invasive. After realizing how nice it smelled I actively looked for it when out walking the dogs and never found much.