The principal North American Labrador tea, L. palustre subsp. groenlandicum, has a northern transcontinental distribution in North America, occurring from coast to coast in Canada, and occasionally north of the tree line. It has been locally naturalized in Germany and Great Britain. The plants reside in the mixed temperate and boreal vegetation zones of North America. The European version of Labrador tea, marsh tea, has been shown to be chemically different from the main North American Labrador tea, and indeed appears to have poisonous properties and to be capable of causing abortion. Astringent (mouth-puckering) tannins are present in Labrador tea and, indeed, are also in the most common hot beverages: tea, coffee, and cocoa. They have been experimentally shown to interfere with digestibility of proteins and to have carcinogenic potential, but there is little evidence of adverse effect in humans.