They call him Goathead Greg and he has uprooted 427.5 pounds of puncture vine from Denver bike...

People who’ve never had a flat tire move to Denver and find themselves patching bike tubes — sometimes several times per ride.

They wonder: What’s going on?

At first, they blame their tires, broken glass, or bad luck. Little do they know, here in the high plains desert, where the soil is dry and rain is rare, a diabolical plant with horned seeds is conspiring to slow them down.

Children and pets step on the thorny pods and cry. Gardeners try to pull these plants up as fast as they grow. The seeds cling to shoe soles and pants cuffs and spread into homes and down sidewalks, birthing plants that stretch across unirrigated soil and crack through concrete.