A cool and somewhat unexpected new discovery desterday evening, the shortleaf or catsclaw sensitive plant, Mimosa microphylla.
This is a native species of sensitive plant. The reason these are called sensitive plants is due to the interesting reaction of their leaves to touch: they fold themselves up for protection, or if the plant finds that conditions aren't absolutely ideal for it. This movement is fairly rapid and noticeable.
This plant has the interesting nickname of catsclaw sensitive plan due to the fact that it REALLY does not like to be touched. Not only will it's leaves fold up and try to hide from you, but the stems have large, very sharp, deeply hooked thorns that are effectively the same size and shape as, you guessed it, the claws of a cat.