Involved in the biosynthesis of labdane-type diterpenoid including marrubiin and other labdane-related furanoid diterpenoids with potential applications as anti-diabetics, analgesics or vasorelaxants (Probable). May be involved in the conversion of geranylgeranyl diphosphate (GGPP) to ent-copalyl diphosphate (ent-CPP) and 8-hydroxycopalyl diphosphate (LPP, labda-13-en-8-ol diphosphate) (Probable). Plant hormone biosynthesis; gibberellin biosynthesis. Secondary metabolite biosynthesis; terpenoid biosynthesis. Present in both leaves and flowers. The Asp-Xaa-Asp-Asp (DXDD) motif is important for the catalytic activity, presumably through binding to Mg(2+). Belongs to the terpene synthase family.