Acorales, the sweet flag order of flowering plants and the most basal lineage among themonocotyledons (monocots), which are characterized by having a singleseed leaf. This order contains the single family Acoraceae and onegenus (Acorus), whichcomprises two to four species of plants that resemble theirises.

Acorus calamus (sweet flag) occurs in the wetlands ofNorth America and fromIndia to Indonesia. Other species are distributed in temperate areas inAsia andEurope, where they are often found at pond margins or along fast-moving streams.

Sweet flag has been used as an herbal ingredient at least since the Classical Greek era. BothA. calamus andA. gramineus are commonlycultivated as ornamentals in gardens.

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Acorus was formerly placed in the family Araceae because of the clustering of the minute, perfect (bisexual) flowers into a spadix, but it was later realized thatAcorus differs in several respects—notably, in having unifacial rather than bifacial leaves, introrse rather than extrorse anthers (with the anther opening toward the inside of theflower rather than toward the outside), dry rather than fleshy fruits,ethereal oils and not raphides, and apical rather than basal placentation. In addition, investigations employingDNA sequencing techniques have shown that this genus is distinctive from the Araceae and should be placed as the basal lineage to all other monocots. Given these morphological and genetic differences, a separate family and order are considered justified by most botanists.