AHA I found a pic for you - CLICK THIS - it loads a bit slow but worth looking at - Burr medic
this is what WE had in our yard and here in houston...(see how you can't SEE the burrs ?) It kinda looks like Clover -
the first pic is alot of plants or one really BIG one - they grow over the ground I think - I used to have little ones and those suckas were JACKED OUT OF THE GRASS BY ME everytime I saw one -
search the net and you can find more pics -