Oral Paper

         Paleobotany

Paleogene evidence for anatomically preserved gleicheniaceous pinnules with sori in marine carbonate concretions from Vancouver Island, B.C., Canada

Presenting Author
Gar Rothwell
Description
            Gleicheniaceae has what may be the longest fossil record of all leptosporangiate families with living representatives. Nevertheless, anatomically preserved fertile structures are extremely rare from Cenozoic deposits. Fertile frond fragments with abaxially attached radial sori recently have been recognized in a diverse assemblage of plant remains preserved in carbonate marine concretions at the Paleocene-Eocene Appian Way collecting locality along the eastern margin of Vancouver Island, British Columbia, Canada. Pinnule fragments with a lamina ~70 µm thick and relatively homogeneous mesophyll anatomy bear sori of seven to nine annulate sporangia. Sori are positioned below a vein, and are exindusiate with a receptacle that bears sporangia both laterally and terminally. Each sporangium has an ovoid capsule up 120 µm in maximum diameter and 155 µm long, and an extremely short, broad stalk.  An oblique, uniseriate annulus makes up much of the capsule wall, but there are thin-walled cells along one side that form a stomium. Most sporangia are senescent, but one contains oval-radial trilete spores 13 - 18 µm in diameter with a thin wall that appears psilate under light microscopy. These fertile structures accompany vegetative organs at the Appian Way locality that have been described as Gleichenia appianensis. Rhizomes of G. appianensis have a marginally mesarch stolid protostele and attached adventitious roots, and the frond segments have pseudo-dichotomous branching and C-shaped traces with infolded adaxial hooks. Because only one type of gleicheniaceous rhizome, vegetative frond, and fertile pinnule have been discovered within the extensively sampled and studied floral assemblage at the Appian Way locality, it is reasonable to suspect that all of those organs were produced by a single species of gleicheniacous ferns.  If correct, this material represents the most complete gleicheniaceous plant in post Mesozoic fossil record. These fossils also document that essentially modern species of Gleicheniaceae evolved no later than the base of the Cenozoic.