Acorus is agenus ofmonocotflowering plants. This genus was once placed within the familyAraceae (aroids), but more recent classifications place it in its own familyAcoraceae and orderAcorales, of which it is the sole genus of the oldest surviving line of monocots. Some older studies indicated that it was placed in a lineage (the order Alismatales), that also includes aroids (Araceae),Tofieldiaceae, and several families of aquatic monocots (e.g., Alismataceae,Posidoniaceae). However, modern phylogenetic studies demonstrate thatAcorus issister to all other monocots. Common names includecalamus andsweet flag.
The genus is native toNorth America and northern and easternAsia, andnaturalised in southern Asia andEurope from ancient cultivation.[2][3][4][5][6][7] The known wild populations arediploid except for sometetraploids in eastern Asia, while the cultivated plants are steriletriploids, probably ofhybrid origin between the diploid and tetraploid forms.
The inconspicuousflowers are arranged on a lateralspadix (a thickened, fleshy axis). Unlike aroids, there is nospathe (large bract, enclosing the spadix). The spadix is 4–10 cm long and is enclosed by the foliage. The bract can be ten times longer than the spadix. Theleaves are linear with entire margin.
Although the family Acoraceae was originally described in 1820, since thenAcorus has traditionally been included in Araceae in most classification systems, as in theCronquist system. The family has recently been resurrected as molecular systematic studies have shown thatAcorus is not closely related to Araceae or any othermonocot family, leading plant systematists to place the genus and family in its own order. This placement currently lacks support from traditional plant morphology studies, and some taxonomists still place it as a subfamily of Araceae, in the orderAlismatales. TheAPG III system recognizes order Acorales, distinct from the Alismatales, and as thesister group to all other monocots. This relationship is confirmed by more recent phylogenetic studies.[8][9] Treatment in theAPG IV system is unchanged from APG III.[10]
In older literature and on many websites, there is still much confusion, with the nameAcorus calamus equally but wrongly applied toAcorus americanus (formerlyAcorus calamus var.americanus).
The Kew Checklist accepts 4 species within the genus Acorus:[2]
Acorus calamusL. – common sweet flag; sterile triploid (3n = 36); probably of cultivated origin. It is native toIrtysh River valley,Kazakhstan but has been widely cultivated and naturalised elsewhere includingEurope, eastern North America, temperateIndia and theHimalayas and southernAsia.[11]
Acorus americanusRaf. - Canada, northern United States, Siberia to Inner Mongolia.[12]
Acorus gramineusSol. exAiton – Japanese sweet flag or grassy-leaved sweet flag; fertile diploid (2n = 18); - China, Himalayas, Japan, Korea, Indochina, Philippines, Primorye.[13]
The name 'acorus' is derived from the Greek word 'acoron', a name used byDioscorides, which in turn was derived from 'coreon', meaning 'pupil', because it was used inherbal medicine as a treatment forinflammation of theeye.[citation needed]
These plants are found inwetlands, particularly marshes, where they spread by means of thick rhizomes. Like many other marsh plants, they depend uponaerenchyma to transport oxygen to the rooting zone.[15] They frequently occur on shorelines and floodplains where water levels fluctuate seasonally.
The native North American species appears in many ecological studies. Compared to other species of wetland plants, they have relatively high competitive ability.[16] Although many marsh plants accumulate large banks of buried seeds,[17] seed banks ofAcorus may not accumulate in some wetlands owing to low seed production.[18] The seeds appear to be adapted to germinate in clearings; after a period of cold storage, the seeds will germinate after seven days of light with fluctuating temperature, and somewhat longer under constant temperature.[19] A comparative study of its life history traits classified it as a "tussock interstitial", that is, a species that has a dense growth form and tends to occupy gaps in marsh vegetation, not unlikeIris versicolor.[20]
Sweet Flag (2006 drawing by USGS Northern Prairie Wildlife Research Center)
Products derived fromAcorus calamus were banned in 1968 as food additives by the United StatesFood and Drug Administration.[21] The primary chemical responsible for the plant's toxic and carcinogenic effects isβ-asarone. Confusion exists whether all strains ofA. calamus contain this substance.
Four varieties ofA. calamus strains exist in nature: diploid, triploid, tetraploid and hexaploid.[22] Diploids do not produce the carcinogenic β-asarone. Diploids are known to grow naturally in Eastern Asia (Mongolia and C Siberia) and North America. The triploid cytotype probably originated in the Himalayan region, as a hybrid between the diploid and tetraploid cytotypes.[23] The North American Calamus is known asAcorus calamus var.americanus or more recently as simplyAcorus americanus. Like the diploid strains ofA. calamus in parts of the Himalayas, Mongolia, and C Siberia, the North American diploid strain does not contain the carcinogenic β-asarone.[24][25][26] Research has consistently demonstrated that "β-asarone was not detectable in the North American spontaneous diploidAcorus [calamus var.americanus]".[27]
The parallel-veined leaves of some species contain ethereal oils that give a sweet scent when dried.[citation needed] Fine-cut leaves used to be strewn across the floor in the Middle Ages, both for the scent, and for presumed efficacy againstpests.[citation needed]
^Govaerts, R. & Frodin, D.G. (2002). World Checklist and Bibliography of Araceae (and Acoraceae): 1–560. The Board of Trustees of the Royal Botanic Gardens, Kew.
^Boyce, P.C., Sookchaloem, D., Hetterscheid, W.L.A., Gusman, G., Jacobsen, N., Idei, T. & Nguyen, V.D. (2012). Flora of Thailand 11(2): 101–325. The Forest Herbarium, National Park, Wildlife and Plant Conservation Department, Bangkok.
^Marongiu, L.B; Piras, A; Porcedda, S (2005). "Chemical composition of the essential oil and supercritical CO2 extract of Commiphora myrrha (Nees) Engl. and ofAcorus calamus".Journal of Agricultural and Food Chemistry.53 (20):7939–43.Bibcode:2005JAFC...53.7939M.doi:10.1021/jf051100x.PMID16190653.
Govaerts, R. & Frodin, D.G. (2002). World Checklist and Bibliography of Araceae and Acoraceae. 1–560. The Board of Trustees of the Royal Botanic Gardens, Kew.
Soltis, D. E.; Smith, S. A.; Cellinese, N.; Wurdack, K. J.; Tank, D. C.; Brockington, S. F.; Refulio-Rodriguez, N. F.; Walker, J. B.; Moore, M. J.; Carlsward, B. S.; Bell, C. D.; Latvis, M.; Crawley, S.; Black, C.; Diouf, D.; Xi, Z.; Rushworth, C. A.; Gitzendanner, M. A.; Sytsma, K. J.; Qiu, Y.-L.; Hilu, K. W.; Davis, C. C.; Sanderson, M. J.; Beaman, R. S.; Olmstead, R. G.;Judd, W. S.; Donoghue, M. J.;Soltis, P. S. (8 April 2011). "Angiosperm phylogeny: 17 genes, 640 taxa".American Journal of Botany.98 (4):704–730.Bibcode:2011AmJB...98..704S.doi:10.3732/ajb.1000404.hdl:2027.42/142064.PMID21613169.
