This report focuses on the Russian thistle, an invasive plant species that has spread rapidly in California since its introduction in the 19th century. The report describes the biology and ecology of the thistle, as well as its economic and environmental impacts. It also provides an overview of the laws and measures that have been implemented to control the thistle, as well as information on two related species, the Canada and Scotch thistles. This work has been selected by scholars as being culturally important, and is part of the knowledge base of civilization as we know it. This work is in the "public domain in the United States of America, and possibly other nations. Within the United States, you may freely copy and distribute this work, as no entity (individual or corporate) has a copyright on the body of the work. Scholars believe, and we concur, that this work is important enough to be preserved, reproduced, and made generally available to the public. We appreciate your support of the preservation process, and thank you for being an important part of keeping this knowledge alive and relevant.