The comparative morphology of 8 species of Lycopodiuln from Northwestern Argentina has been studied. Theoe species are: L. clavatwn L., L. mandiocanuln Raddi, L. lnagel1anicwn (P.B.) Sw., L. sanctoe·barbarae Rolleri, L. saururus Lam., L. sotae Rolleri, T,. subulatllln Desv. and L thyoides H. B. Willd. Characters under consideration are: morphologic types of the sporophyte, adult root, stem axis, lea ves and fertile structure. Aspects investigated by other authors -gametophyte, embryology and cytology- are also commented. The following conclusions, partial as well as general, arise from the undertaken research.Facultad de Ciencias Naturales y Museo