| Mesozoic Osmundaceae petrified stems are often referred to the genera Ashicaulis Tidwell 1994 or Millerocaulis Erasmus ex Tidwell emend. Tidwell 1994, depending only on the presence or absence of leaf gaps in the xylem cylinder. However, this character is problematic for generic distinctions, since some specimens (as in the living Osmundaceae) present or lack these structures, depending on the place where the plant was cut. Furthermore, different authors have identified leaf gaps in some specimens where others reported the absence of these structures. Since this generic separation often leads to incomplete comparisons between the species, it is proposed to combine Ashicaulis Tidwell 1994 and Millerocaulis Erasmus ex Tidwell emend. Tidwell 1994 in... |
