Maslova, E.V. & M.S. Ignatov. On the costa variation in leaves of Protoshagnalean mosses of Permian
Arctoa (2013) 22: 61-68
Leaves of extinct mosses of the order Protosphagnales are studied with the special attention to their different developmental stages. A previously unknown morphotypes without costa and with very short costa are revealed in this group. It is characteristic for young small leaves of Kosjunia and Intia, but apparently does not occur in other genera of this fossil order. The present collection allows restore a heteroblastic series in these leaves and associated with it differentiation of laminal areolation.