Press R to reset, or as a emergency button if the plants get out of control.
If you can spot a categorizable behaviour please explain it in the comments!
There are 3 initial seeds, two of which are identical with a medium height stem a medium growing rate, the third one have a low steam and very slow growing rate.
UPDATE (25 July 2013): Problem fixed with a custom Unity "universal" loader, added R key to reset.
UPDATE (16 April 2021): New version available, check http://www.alejolab.com/blog/alien-plants-in-back