In June of 2006 Colorado Department of Agriculture's Conservation Services Division issued updated Rules pertaining to the administration and enforcement of the Colorado noxious weed act  (8 CCR 1206-2). The Colorado Noxious Weed Act is contained in §§35-5.5-101 through 119, C.R.S. (2003) and applies to everyone in Colorado. Three lists of noxious weeds are specified in the act and the updated rules specify which plants are currently on each of these lists. The worst noxious weed offenders are on List A (Category 1) and must be eradicated throughout the state. List B (Category 2) noxious weeds must be managed. Future plans being developed related to noxious weeds on List C (Category 3) are to provide additional education, research, and biological control resources to jurisdictions that choose to require management of these species. Now, simply click on the name of each list to see photographs of all of the plants on it!

These pages will assist those affected by the Colorado Noxious Weed Act in visually identifying plants that they must eradicate and/or manage. Plants on each of the lists are in alphabetical order by their Common name, with their scientific name always given in parenthesis. When available, click on the highlighted plant name to see a US based fact sheets for that weed. In preparing this guide the best free photographs from around the world, available on the Internet, were used as sources. Photos were enhanced, as necessary, to help viewers identify Colorado noxious weeds with minimal effort. To visit the source site for each picture, simply click on it. Most of these worthy source sites, belong to local and state governments, universities, botanical gardens, non-profit organizations or individual photographers. They are full of interesting documentation and are worth browsing for additional information on botany, weeds, plants and other related issues. (Some of the sites from Canada, France, Belgium, Norway, Germany, Czech, Poland, Japan and etc. unfortunately do not have their pages available in English.)

Invasive Species are considered to be "any species of insects, animals, plants and pathogens, including its seeds, eggs, spores, or other biological material capable of propagating that species, that is not native to that ecosystem; and whose introduction does or is likely to cause economic or environmental harm or harm to human health." Please note that his definition applies equally to native species, as well as those that were introduced. Curiously, some of the weed species that are considered noxious in Colorado are very much admired for their beauty flowers, medicinal use, and even food value (yes, some are edible!) in other parts of the world. Of course, many are very poisonous to humans and/or domestic animals.