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Probably indigenous to most of Asia, the triploid form "Acorus calamus" var. "calamus" (also known as var. "vulgaris" or var. "verus") has now been introduced across Europe, Australia, New Guinea, South Africa, Réunion and North America. The tetraploid form "Acorus calamus" var. "angustatus" is native throughout Asia, from India to Japan and the Philippines and from Indonesia to Siberia. The diploid form "Acorus americanus" or "Acorus calamus" var. "americanus" is found in northern subarctic North America and scattered disjunct areas throughout the Mississippi Valley, and furthermore diploids are also found in Mongolia, central Siberia (Buryatia), Gilgit–Baltistan in Pakistan (claimed by India) and northern Himachal Pradesh in India. It is extinct in some parts of the United States and Canada. It may not been native to some of these areas, Pre-Columbian populations are thought to have dispersed it across parts of the United States.