Originally Posted by stevepusser

One plant can make thousands of these caltrops-style thorns, shaped so that one thorn is always pointed up. It's a low, spreading plant with small yellow flowers, and like to grow in bare, disturbed soil, such as roadsides. They love warm weather, and at least here in SoCal, seem to suck any moisture they need from the humidity in the air, in that they can grow wildly on bare soil during our rainless summer. They are not native to the Americas, so don't feel guilt about destroying them here. They can't get through car tires, but any activity on the shoulder can spread hundreds onto the paved surface to lie in wait for you. You also have to be careful about rolling your bike anywhere off road, or use tire liners or thick tread to defeat them.

Tribulus terrestris - Wikipedia, the free encyclopedia