Sesquiterpene synthase converting farnesyl diphosphate to six sesquiterpenes, with beta-elemene, delta-cadinene and an unidentified oxygenated sesquiterpene as the major products. Has no diterpene synthase activity. Binds 3 Mg(2+) ions per subunit. Secondary metabolite biosynthesis; terpenoid biosynthesis. Up-regulated by alamethicin treatment. The Asp-Asp-Xaa-Xaa-Asp/Glu (DDXXD/E) motif is important for the catalytic activity, presumably through binding to Mg(2+). Selaginella moellendorffii contains two distinct types of functional terpene synthases (TPS) genes, the typical seed plants TPS genes (SmTPSs) and a microbial type TPS genes (SmMTPSLs). Belongs to the terpene synthase family.