Patents on plants: http://www.patentgenius.com/class/PLT.html
Yes, you read that right - plants can now be patented!
"Plants ... are patentable under Title 35 U.S. Code, Section 161, which provides for the granting of a patent to whoever invents or discovers and asexually reproduces any distinct and new variety of plant, including cultivated sports, mutants, hybrids, and newly found seedlings other than a tuber propagated plant or a plant found in an uncultivated state."
This site lists patented plant varieties (over 18,000 as of Nov 11). These are the plants you see in garden centres with labels prohibiting propagation.