Or, Know Thy Enemy: Tribulus terrestris, puncturevine, goat's head burr, devil's head burr, caltrop burr, Mexican sand burr.
This nasty piece of work has made an appearance out on my parkway at the corner. Even since I first spotted it earlier this summer, I've been checking the area every few days and pulling every seedling I could find. Inevitably a few escaped my notice and grew big enough to present a real danger.
This flower has closed up since I pulled it. I didn't take any photos in situ because when I see this weed, I have to pull it right then.
Those pretty little flowers become spiky fruits. Already they're painful to touch.
Once they've dried out, the fruits split into individual burrs with the distinctive shape that lends the plant some of its many names.
They're the devil, I tell you!
The seeds can remain viable for 5-7 years. That's why it's important to kill the plant as soon you recognize it. You may remember my original post about the caltrop, a medieval weapon (as well as an interesting nut). Reportedly the caltrop burr itself has been used as a weapon in Africa, its spines coated with poison and the burrs left where someone is likely to tread on them.
Since they're sharp enough to puncture a bike tire, you know they're a danger to anyone walking barefoot. When Sophie steps on one, she stops immediately and waits for me to remove it.
If you see this weed in your yard, pull it pronto!