spring-loaded harpoon weeds 

(Source:io9.com)

The Redstem filaree is a weed spreading out of control because of its mechanical abilities. Its seeds are natural coils. As they grow they develop more tension until they overpower their parent plants and fling themselves outward with tremendous energy.
Once they hit the ground, they embed harpoon-like in the soil. When moisture increases they unfurl, driving themselves deeper, and when they dry out, a series of angled hairs prevent them from retracting.
New research accurately calculates how far and fast they can grow, accounting for their virulent spread in Southwestern parts of the U.S. How can you defeat a plant whose reproductive cycle is so weaponized?

Send an email to Tim Barribeau, the author of this post, at tim@io9.com.