Arabidopsis thaliana , or the mouse-ear cress, is to plant sciences, what mouse is to animal biology. It has all features to make it a perfect model organism and has, despite several recent genome duplications, a very small genome. Additionally several techniques to manipulate these plants and their genome made it the perfect candidate to be the first plant to have it’s genome sequenced.

Further reading:

Analysis of the genome sequence of the flowering plant Arabidopsis thaliana. Nature 408, 796-815 (2000). [pubmed]