This is a companion photo gallery to Flowering Plants of the Arroyo Seco and is the first one I have ever done that is composed entirely of introduced species. It includes only non-native plants, which although originally brought from elsewhere have in many cases outcompeted native plants and spread over vast areas. Nevertheless they are interesting and often beautiful in their own right. Most introduced plants in Southern California have originated from areas that share a similar type of climate such as the Mediterranean basin, South Africa, Australia, South America, and simply because of its proximity, Mexico. The website of the California Department of Fish and Wildlife says this: "California hosts approximately 1,100 species, subspecies, and varieties of plants that did not naturally occur in the state, but have become naturalized and continue to reproduce in the wild. Of these, approximately 183 are currently listed on the Pest Ratings of Noxious Weed Species and Noxious Weed Seed developed by the California Department of Food and Agriculture, which categorizes them as invasive plants capable of damaging the environment and economy of our state. Invasive plants not only crowd out crops, degrade rangeland, increase the potential for wildfire and flooding, consume valuable water, and degrade recreational opportunities, but they also pose a serious threat to California’s native plant species. Invasive plants tend to out-compete California’s native flora for resources such as space, light, water, and nutrients, are sometimes avoided by animals which can cause an increase in pressure on native plants, and can entirely replace natural vegetation communities." Introduced species often have several advantages over native ones. They have left behind a complex network of specialized predators, parasites and diseases, they often grow faster, mature sooner and produce more offspring, they typically are generalists capable of surviving in a variety of degraded soils, and they sometimes release toxic substances into the ground that inhibit the plants already there. Although introduced and non-native, what are called naturalized species are those that have successfully reproduced and established self sustaining populations in the wild without displacing native species. Many introduced species are mostly seen in proximity to human habitation where they have been planted in people's gardens. Despite the length of this gallery and the number of taxa it includes, there are undoubtedly many others that I simply have no pictures of, and keep in mind that many if not most of these taxa are likely to be found in areas of the watershed closer to population centers.