Abstract Little is known about the floral or pollination biology of Acorus, the basal lineage of the monocots. In this study we investigated chemical profiles of the floral scents to better understand the reproductive biology of Acorus. Headspace volatiles emitted from the spadices (flowers) and leaves of Acorus gramineus and Acorus calamus native to Japan were collected and analyzed by GC–MS. The GC–MS profiles clearly indicated that the spadix of A. gramineus emitted a considerable amount of volatiles, whereas A. calamus emitted a small amount equivalent to the leaf volatiles. The main floral scent volatile in A. gramineus was 2-(1E,3Z-hexadienyl)tetrahydrofuran (ca. 80–90%) which was identified by NMR analysis. The compound has never been reported elsewhere as a natural product. These data and previous studies examining the reproductive biology of Acorus suggest that A. gramineus seems to be entomophilous. It is known that Japanese A. calamus is sterile (tetraploid), which may explain its reduced emission rate of floral volatiles.