A new specimen of Millerocaulis (Osmundales: Osmundaceae) from the Cerro Negro Formation (Lower Cretaceous), Antarctica

a new petrified stem of millerocaulis erasmus ex tidwell emend. vera, collected in the aptian cerro negro formation outcrops of livingston island (antarctica), is described in detail. this specimen is probably conspecific with millerocaulis australis (vera), from the same unit, but it is smaller than the holotype and only known specimen of the latter species. furthermore, differences between several characteristics of both specimens are observed. a discussion based on biological aspects of this group of plants is given, taking into account the ontogenetic variability. a conservative referral of the new specimen to m. australis is preferred over the proposal of a new morphotaxon for the inclusion of the new materials.