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The Acorus calamus group, or sweet flag, includes important medicinal plants and is classified into three species: A. americanus (diploid), A. verus (tetraploid), and A. calamus (sterile triploid of hybrid origin). Members of the group are famous as components of traditional Indian medicine, and early researchers suggested the origin of the sweet flag in tropical Asia. Subsequent research led to an idea of the origin of the triploid A. calamus in the Amur River basin in temperate Asia, because this was the only region where both diploids and tetraploids were known to co-occur and be capable of sexual reproduction. Contrary to this hypothesis, triploids are currently very rare in the Amur basin. Here, we provide the first evidence that all three species occur in Kazakhstan. The new records extend earlier data on the range of A. verus for c. 1800 km. Along the valley of the Irtysh River in Kazakhstan and the adjacent Omsk Oblast of Russia, A. verus is recorded in the south, A. americanus in the north, and A. calamus is common in between. We propose the Irtysh River valley as another candidate for a cradle of the triploid species A. calamus. It is possible that the range of at least one parent species (A. americanus) has contracted through competition with its triploid derivative species, for which the Irtysh River floods provide a tool for downstream range expansion. We refine our earlier data and show that the two parent species have non-overlapping ranges of variation in a quantitative metric of leaf aerenchyma structure. [ABSTRACT FROM AUTHOR]

Commonly considered bispecific, Acorus is one of the most phylogenetically isolated angiosperm genera that forms the order Acorales sister to the rest of the monocots. The Acorus calamus group is widely distributed in the Holarctic regions of Eurasia and America and has strong medicinal and other practical uses since prehistoric times. Earlier studies interpreted native diploids and invasive triploids occurring in North America as two species that differed in morphology and distribution ranges. In contrast, diploids, triploids, and tetraploids occurring in Eurasia are commonly interpreted as one species because they reportedly cannot be distinguished in collections. We resolve the controversy over taxonomic concepts between Eurasia and America and provide the first detailed multidisciplinary account of Acorus in temperate Asia. We used plastid and nuclear markers, leaf anatomy, seed micromorphology, pollen stainability, flow cytometry, and direct chromosome counts. Diploids and tetraploids show stable molecular and micromorphological differences. Triploids are their sterile hybrids, with the plastid genome inherited from the diploid parent. Diploids of America and Asia tend to differ in leaf characters. Coadaptative coexistence with pollinating beetles Platamartus jakowlewi and Sibirhelus corpulentus (Kateretidae) is conserved between diploids and tetraploids and over a distance of 4700 km between Japan and Western Siberia. Diploids are self‐compatible and can set seeds in the absence of kateretid beetles. Tetraploids are self‐incompatible and/or cannot set seeds in the absence of Platamartus and Sibirhelus. Diploids (A. americanus) and tetraploids (A. verus) are two biological species; the former has two subspecies. Acorus calamus should be restricted to triploids; it apparently first evolved in temperate Asia. Diploids mostly occur in much cooler climates than triploids and tetraploids. Accessions of A. verus and A. calamus from tropical Asia are apparently derived from ancient introductions. Our data provide a new framework for the pharmacological use of Acorus. [ABSTRACT FROM AUTHOR]

The basal monocot genus Acorus comprises essential oil-producing plants widely used in traditional medicine in various countries, including India. Acorus calamus sensu lato is a polyploid complex where the essential oil composition, to some extent, depends on the ploidy level. The literature recognizes diploids (in temperate Asia and North America), triploids (Asian in origin, naturalized elsewhere) and tetraploids (temperate to tropical Asia) at the rank of varieties of A. calamus. We show that the current use of the name A. calamus var. angustatus for the tetraploids is not properly justified. The earliest name based on the Asian material is A. calamus var. verus published in 1753 by Linnaeus. We justify the use of the Linnaean variety for tetraploids by selecting an epitype based on the material cultivated in Peninsular India, for which direct chromosome counts are provided. The name A. verus is available if the tetraploid cytotype is recognized at the species rank. We support earlier data on the importance of leaf anatomy for cytotype diagnostics in Acorus, but also show the limitations of the use of this approach. The growth pattern of the tropical Indian tetraploid material is discussed, and the evergreen nature of the accession studied here is documented. The exact chromosome number of the tetraploid Acorus requires further clarification. All metaphase plates examined here showed at least 44 chromosomes, but plates apparently showing more than 44 chromosomes were found as well. They may be explained by technical difficulties in counting chromosomes in Acorus. Alternatively, our data may indicate the occurrence of aneuploid mixoploidy. [ABSTRACT FROM AUTHOR]

Heinrich Wilhelm Schott (1794–1865) was one of the pioneering researchers in the taxonomy of the species-rich monocot family Araceae. He described numerous new plant species in various genera, including Acorus, which is currently segregated as a monogeneric family and order occupying a position sister to the rest of the monocots. While describing his new species of Acorus, Schott mostly used characters that are currently considered of low, if any, taxonomic value. His descriptions lack some key characters including, for obvious reasons, chromosome numbers. Therefore, Schott's species concepts cannot be properly interpreted according to the current understanding of the taxonomic diversity of Acorus, even though his species names must be examined for implementation of the principle of nomenclatural priority. The only way of resolving the taxonomic identity of Schott's species names is through the identification of type specimens among historical herbarium collections, by inferring taxonomically significant characters that are missing in Schott's descriptions. On the basis of herbarium collections of the Komarov Botanical Institute, St. Petersburg (LE), we were able to infer ploidy levels of the materials used by Schott to describe Acorus triqueter (diploid, Siberia), A. tatarinowii (tetraploid, China), A. nilaghirensis (tetraploid, India), A. griffithii (tetraploid, Bhutan), and A. commutatus (tetraploid, Bhutan). Leaf anatomy and pollen stainability were used as cytotype markers. All five species belong to the polymorphic Acorus calamus complex that comprises important medicinal plants. Detailed historical and nomenclatural analyses of Schott's species names and herbarium collections are provided. [ABSTRACT FROM AUTHOR]

The article discusses the nomenclature of Acorus calamus var. americanus (A. americanus) and proposes to conserve the name with a conserved type. Acorus species have practical uses in herbal medicine, pharmacology, and other industries. The article provides evidence that A. americanus is a diploid plant, not a triploid as previously believed. The authors propose to retain the name A. americanus for the diploid species and designate a specific collection as the conserved type. They argue that replacing the established name with a long-obsolete one would create confusion and propose to fix the current nomenclatural status quo. [Extracted from the article]