A plant is introduced if it was brought here by humans. Many culinary and medicinal herbs were also introduced into this country by Europeans. A plant that escapes from cultivation and thrives on its own in the wild is considered naturalized. Catnip and motherwort are examples of plants that were introduced by Europeans as medicinal herbs, but which now grow everywhere. Queen Anne's Lace is actually the second-year flower of the carrot, escaped from gardens and growing wild.
Wild parsnip is also a garden escapee that grows very well in ditches in Minnesota.
Some plants are invasive, displacing the native vegetation because they compete well, and are not kept in check by balanced relationships with other organisms. If they displace the native vegetation, lack of native plants may reduce the populations of other organisms in the community which depend on them, causing displacement or local extinction. Examples of invasive exotic species that are major problems in Minnesota include European buckthorn, a shrub that was introduced as a hedge-forming shrub and is now displacing native vegetation in woodlands, and purple loosestrife, which escaped from flower gardens and is now taking over native plants and riverbanks, eliminating diversity in these areas. Native plant source book. Practically speaking, the easiest way is to find a copy of Ownbey and Morley's Vascular Plants of Minnesota.