Acorus

Lore & Background

The genus Acorus was once placed within the family Araceae (aroids), but more recent classifications place it in its own family Acoraceae and order Acorales. Some older studies indicated placement in Alismatales, but modern phylogenetic studies demonstrate that Acorus is sister to all other monocots. The inconspicuous flowers are arranged on a lateral spadix, and unlike aroids, there is no spathe. Acorus species lack typical vessel elements in their xylem, relying instead on tracheids, a trait considered evolutionarily primitive.

The genus is native to North America and northern and eastern Asia, and naturalised in southern Asia and Europe from ancient cultivation. Known wild populations are diploid except for some tetraploids in eastern Asia, while cultivated plants are sterile triploids, probably of hybrid origin. The name 'acorus' is derived from the Greek word 'acoron', used by Dioscorides, from 'coreon' meaning 'pupil', due to its use in herbal medicine for eye inflammation.

These plants are found in wetlands, particularly marshes, where they spread by thick rhizomes and depend upon aerenchyma to transport oxygen to the rooting zone. They frequently occur on shorelines and floodplains where water levels fluctuate seasonally. The native North American species has relatively high competitive ability compared to other wetland plants, and its seeds are adapted to germinate in clearings after cold storage.

Reader's Guide

Acorus holds significance as the sole genus of the oldest surviving line of monocots, a position confirmed by modern phylogenetic studies and recognized in the APG III and APG IV systems. Its evolutionary primitiveness is underscored by its lack of typical vessel elements in xylem, relying instead on tracheids. The genus has a complex taxonomic history, having been traditionally included in Araceae until molecular studies revealed its distinctness, leading to its placement in its own order, Acorales. This placement lacks support from traditional plant morphology, and some taxonomists still place it as a subfamily of Araceae in Alismatales. The Kew Checklist accepts four species: Acorus calamus, Acorus americanus, Acorus gramineus, and Acorus verus. Confusion persists in older literature, with the name Acorus calamus wrongly applied to Acorus americanus. Products derived from Acorus calamus were banned in 1968 as food additives by the United States Food and Drug Administration due to the carcinogenic compound β-asarone, though diploid strains from North America and parts of Asia do not contain this substance. The leaves contain ethereal oils that give a sweet scent when dried, and were historically strewn across floors in the Middle Ages for scent and pest control.

Did You Know?

• Acorus is the sole genus of the family Acoraceae and order Acorales, sister to all other monocots.
• Cultivated Acorus plants are sterile triploids, probably of hybrid origin between diploid and tetraploid forms.
• The North American diploid strain of Acorus does not contain the carcinogenic β-asarone.
• The name 'acorus' derives from the Greek word 'acoron', used by Dioscorides for eye inflammation treatment.