Acorus calamus has already been reported based on a single specimen collected from Guilan province. Yet, this species has not been reported during last 50 years in Iran and thus, its herbarium specimen is not available. A sample of the species was collected from southern area of Sari during a study on aquatic plants of Mazandaran province. According to the new finding, the natural occurrence of the species was confirmed in Iran. Complementary botanical description, photographs of plant habitat and distribution map of the species were presented. Although, according to the Flora Iranica and Flora of Iran Acorus was considered as a genus of Araceae the recent phylogenetic study considered its taxonomic position in Acoraceae as a distinct family. Therefore, Acoraceae is introduced as a new family to the Flora of Iran with a single representative i. e. Acorus calamus.

Background: Multiple medicinal properties of Acorus calamus, a recently rediscovered plant species in Iran were reported. It is not available any information about chemical composition of essential oil of the species in Iran, therefore such study is necessary.Objective: In this research essential oil composition of aerial parts of three populations of Acorus calamus was studied.Methods: Plant materials were collected from their natural habitats in Mazandaran Province (Arzefoon, Pelesk and Alandan). Essential oils were obtained by hydro distillation and analyzed using GC and GC-MS.Results: In total, 41 components were characterized, and are reported for the first time from Iran. The essential oil yield is 0.5%, 0.45% and 0.48% in Arzefoon, Pelesk and Alandan populations respectively. The main compounds identified in the oils are cis-asarone (27-53%), calamusenone (6.6-9.8%), (E)-caryopyllene (6.3-7.3%), trans-asarone (4.7-6.6%), acorenone (3.6-4.9 %) and (E)-b-farnesene (0.8-5 %).Conclusion: The results revealed that essential oil compositions of three studied populations are quantitative and qualitatively different from each other and also other samples from various origins which could be attributed to their ecological growing factors such as altitude.