What it is: Sweet flag (Acorus calamus) is a perennial wetland herb with a clean, slightly bitter aromatic rhizome. It has been recorded among Chinese aromatic plants since the pre-Qin period. How to use & scenes: Dried rhizome slices are used in sachets, herbal pillows, and traditional incense blends; living plants suit pond edges and damp garden corners. Craft: Rhizomes are harvested in autumn, washed, sliced, and shade-dried or gently dried at low temperature to keep the bitter-sweet scent. Cultural meaning: Sweet flag is tied to riverside customs and early summer traditions in China, representing a quiet, grounded wetland herb.