page_title: Acorus calamus
section_title: Botany
hierarchical_section_title: Acorus calamus / Botany
caption_attribution_description: Name Acorus calamus Family Acoraceae Original book source: Prof. Dr. Otto Wilhelm Thomé Flora von Deutschland, Österreich und der Schweiz 1885, Gera, Germany
context_page_description: Acorus calamus is a species of flowering plant, a tall wetland monocot of the family Acoraceae, in the genus Acorus. Although used in traditional medicine over centuries to treat digestive disorders and pain, there is no clinical evidence for its safety or efficacy – and ingested calamus may be toxic – leading to its commercial ban in the United States.
context_section_description: There are three cytotypic forms distinguished by chromosome number: a diploid form (2n=24), an infertile triploid form (2n=36), and a tetraploid form (see below). The triploid form is the most common and is thought to have arisen relatively recently in the Himalayan region through hybridisation of the diploid with the tetraploid.
  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.
  Currently the taxonomic position of these forms is contested. The comprehensive taxonomic analysis in the Kew World Checklist of Selected Plant Families from 2002 considers all three forms to be distinct varieties of a single species. The Flora of North America publication considers the diploid form to be a distinct species, analyzing North American forms of the diploid variety, and does not analyse the morphology of Asian forms of the diploid variety. Also, in older literature, the name Acorus americanus may be used indiscriminately for all forms of Acorus calamus occurring in North America, irrespective of cytological diversity (i.e. both the diploid and triploid forms). The treatment in the Flora of China from 2010, which is followed in the Tropicos database system, considers all varieties to be synonyms of a single taxonomically undifferentiated species, pointing to morphological overlap in the characteristics singled out by Thompson.
  The primary morphological distinction between the triploid and the North American forms of the diploid is made by the number of prominent leaf veins, the diploid having a single prominent midvein and on both sides of this equally raised secondary veins, the triploid having a single prominent midvein with the secondary veins barely distinct. According to the Flora of China, there is clear overlap in these characteristics and the different cytotypes are impossible to distinguish morphologically. Triploid plants are infertile and show an abortive ovary with a shrivelled appearance. This form will never form fruit (let alone seeds) and can only spread asexually.
  The tetraploid variety is usually known as Acorus calamus var. angustatus Besser. A number of synonyms are known, but a number are contested as to which variety they belong. It is morphologically diverse, with some forms having very broad and some narrow leaves. It is furthermore also cytotypically diverse, with an array of different karyotypes.
caption: Illustration from an 1885 flora by Walther Otto Müller
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