 Strobili are characterized by a central axis (anatomically a stem) surrounded by spirally arranged or decussate structures that may be modified leaves or modified stems.Leaves that bear sporangia are called "sporophylls", while sporangia-bearing stems are called "sporangiophores".Some members of both of the two modern classes of Lycopodiophyta (Lycopodiopsida and Isoetopsida) produce strobili.