Acorus

Acorus
Sweet Flag (Acorus calamus) - spadix
Scientific classification
Kingdom:	Plantae
(unranked):	Angiosperms
(unranked):	Monocots
Order:	Acorales Reveal
Family:	Acoraceae Martinov
Genus:	Acorus L., 1753
Species
See text.

Acorus is a genus of monocot flowering plants. This genus was once placed within the family Araceae (aroids), but more recent classifications place it in its own family Acoraceae and order Acorales, of which it is the sole genus of the oldest surviving line of monocots. The exact relationship of Acorus to other monocots, however, is still debated by scientists. Some studies indicate that it is placed in a lineage (the order Alismatales), that also includes aroids (Araceae), Tofieldiaceae, and several families of aquatic monocots (e.g., Alismataceae, Posidoniaceae). Common names include Calamus and Sweet Flag. It is known as vasambu in Tamil language.

The name 'acorus' is derived from the Greek word 'acoron', a name used by Dioscorides, which in turn was derived from 'coreon', meaning 'pupil', because it was used in herbal medicine as a treatment for inflammation of the eye.

The genus is native to North America and northern and eastern Asia, and naturalised in southern Asia and Europe from ancient cultivation. The known wild populations are diploid except for some tetraploids in eastern Asia, while the cultivated plants are sterile triploids, probably of hybrid origin between the diploid and tetraploid forms.

Taxonomy

Although the family Acoraceae was originally described in 1820, since then Acorus has traditionally been included in Araceae in most classification systems, as in the Cronquist system. The family has recently been resurrected as molecular systematic studies have shown that Acorus is not closely related to Araceae or any other monocot 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 order Alismatales.

The APG II system recognizes order Acorales, distinct from the Alismatales, and as the sister group to all other monocots.

Characteristics

These grasslike evergreen plants are hemicryptophytes, (i.e. perennial plants of which the overwintering buds are at the soil surface) or geophytes (i.e. the overwintering buds are found underground, usually attached to a bulb, corm, tuber, etc.). Their natural habitat is at the waterside or close to marshes, often found with reedbeds.

The inconspicuous flowers are arranged on a lateral spadix (a thickened, fleshy axis). Unlike aroids, there is no spathe (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. The leaves are linear with entire margin.

The parallel-veined leaves of some species contain ethereal oils that give a sweet scent when dried. Fine-cut leaves used to be strewn across the floor in the Middle Ages, both for the scent, and for presumed efficacy against pests.

Species

In older literature and on many websites, there is still much confusion, with the name Acorus calamus equally but wrongfully applied to Acorus americanus.

The genus includes as many as six species:

• Acorus americanus (Raf.) Raf. (formerly known as A. calamus var. americanus) - American Sweet Flag; fertile diploid (2n = 24); occurring in Alaska, Canada and northern USA. Diploid plants in Siberia and temperate Asia may also belong here, but have not been fully investigated (^[1]). Recently recognised as a distinct species by the Flora of North America.
• Acorus calamus L. - Common Sweet Flag; sterile triploid (3n = 36); probably of cultivated origin. It is native to Europe, temperate India and the Himalayas and southern Asia, widely cultivated and naturalised elsewhere.
• Acorus gramineus Sol. ex Aiton - Japanese Sweet Flag or Grassy-leaved Sweet Flag; fertile diploid (2n = 18); occurring in the Himalayas to Japan, Myanmar, Thailand, the Philippines.
• Acorus triqueter Turcz. ex Schott (syn. A. calamus var. angustatus) - fertile tetraploid (4n = 48); occurring in eastern Asia, Japan and Taiwan.
• Acorus latifolius Z.Y.Zhu : native to China
• Acorus xiangyeus Z.Y.Zhu : native to China

Sweet Flag (drawing)

Acorus from Europe, China and Japan have been planted in the United States.

References and external links

• 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.
• Flora of North America: Acorus
• Flora of North America: Acoraceae
• Acorales in Stevens, P. F. (2001 onwards). Angiosperm Phylogeny Website. Version 7, May 2006.
• NCBI Taxonomy Browser
• Acoraceae in L. Watson and M.J. Dallwitz (1992 onwards) The families of flowering plants: descriptions, illustrations, identification, information retrieval. Version: 27 April 2006. http://delta-intkey.com.
• Taxonomy and distribution of Acorus in Maine
• [1]

References