One fellow said sandspurs where a bit different with barbs at the end making them even worse.
It was common when I lived in SoCal to walk around barefoot much of the year. You didn't want to walk into a patch of these. You'd usually have no warning. You'd be walking along, put your foot down and YIKES, the whole bottom of your foot would be covered with them. That hurt, and I recall them making the bottom of my foot itch once they were pulled out.
You couldn't just sit down and start pulling them out because you might sit on a patch of them, too. You'd have to look around for a clear area, then sit down and pull them out of your feet. Ugh!
Sure, shoes protected the feet, assuming you were wearing them, but you still had to pull them out. You can't walk around with two dozen of those stuck to the bottom of your shoe.
They'd get bikes, too. You might not notice at first, but once you got on a hard surface you could hear the noise on the pavement. They could puncture tires, especially the thinner ones like on ten speeds. I don't recall them ever flattening my tires. Maybe because I usually rode a stingray with those wide, knobby, off road type tires.
Whatever they were called, they were quite an adventure. OUCH!