The firmoss (Lycopodium serratum) belongs to the family Lycopodiaceae. It is a perennial pteridophyte that is native to throughout Japan, the Korean Peninsula, China and Southeast Asia. This fern grows on wettish shade places in forests and it can reach 10-20 cm in height. The stems are branched to slightly aslant at the base and extends suberect. The leaves are dark green to lime green, oblong with coarsely toothed margins, and spirally arranged around the stems. The numerous, whitish yellow sori are borne at the axils from September to November. The plant contains the acetylcholinesterase inhibitor huperzine A, and it has been used for centuries in China as a memory enhancer.