HERNANDEZ-CASTILLO, GENARO1*, GAR ROTHWELL2, and GENE MAPES2. 1Department of Biological Sciences, University of Alberta, Edmonton, Alberta, T6G 2E9, Canada; 2Department of Envrionmental and Plant Biology, Ohio University, Athens, Ohio, 45701, USA. - Evidence for compound pollen cones in Paleozoic conifers.
A rich fossil biota from the Upper Pennsylvanian 7-11 mine of eastern
Ohio contains numerous vegetative and fertile compression/impression
specimens that conform to a single species of primitive walchian
conifers. Among these specimens is a compound pollen cone that is
superficially similar to an ultimate vegetative shoot. However,
chemical maceration with HF reveals that the specimen has small
appendages and pollen sacs in the axil of each bract. The cone is
cylindrical, 8.2 cm long, and 0.9 mm in maximum width. Bracts are
simple, linear, 3 - 5 mm long, and 1 - 2 mm wide. Stomata are
distributed across the entire adaxial surface. Bracts subtend a single
axillary dwarf shoot with five to eight sterile scales, and 3-4
sporophylls with terminal pollen sacs. Sterile scales are borne on the
side of the dwarf shoot axis that faces the bract, and laterally. They
overlap each other as if borne in a helical arrangement. Sterile
scales are simple, linear with adaxial stomata. Pollen sacs are
upright, ellipsoidal with a rounded tip. The pollen sacs occur only on
the side of the dwarf shoot that faces the cone axis. Grains
correspond to the sporae dispersae genus Potonieisporites Bharadwaj.
They are monosaccate, with a proximal, bent monolete suture, and a
maximum diameter of 62 - 130 m in polar views. This specimen provides
the first unequivocal evidence that some Paleozoic conifers produced
compound pollen cones that are morphologically equivalent to the
ovulate cones of ancient conifers, and to the pollen cones of
Paleozoic cordaitaleans and modern gnetophytes.
Key words: Compound Pollen Cone, Conifer, Fossil, Paleozoic