Oral Paper

         Paleobotany

An anatomically preserved monocot from the Eocene Appian Way locality of Vancouver Island, British Columbia, Canada

Presenting Author
Gar Rothwell
Description
The biota of Appian Way on the east coast of Vancouver Island contains permineralized fossil plants, gastropods, echinoderms, decapods, bivalves and shark teeth in calcareous concretions that are embedded in a silty mudstone matrix representing a shallow marine environment. The fossil beds unconformably overlie the Late Cretaceous Nanaimo Group strata and are most probably Eocene (ca. 50 Ma) in age. Among the flowering plant remains yet to be described from the locality is a distinctive branching monocot axis with clearly defined tissue zones, leaf bases, and attached roots. The preserved stem segment is at least 5 cm long and ca. 1.5 cm in diameter, with a pith and cortex composed primarily of compact parenchyma and scattered sclereid nests. Lateral branches and adventitious roots diverge from the stem at a wide angle. The pith is surrounded by a vascular cylinder of numerous scattered vascular bundles. Stelar bundles are collateral near the stem center, circular to ovoid, and surrounded by a distinct bundle sheath of smaller cells. Clasping leaf bases in the outer cortex encircle the stem and show several vascular bundles of two distinct sizes. Conducting elements of the xylem, probably narrow diameter vessels, have multiseriate circular bordered pitting and horizontal end walls. Branches have vascular bundles and a pith that are similar to those of the main stem. Roots are vascularized by bundles that extend around the periphery of the vascular cylinder before entering the diverging root. Each root has a polyarch stele that consists of radiating rays of xylem and phloem that surround a parenchymatous pith. Differentiation of an endodermis and an outer rhizodermis are not evident, but roots do have a well-defined zone of sclerotic cortex that shows no evidence of aerenchyma. Intact anatomically preserved monocot stems, like the Appian Way specimen, are rarely encountered as fossils. The most well-known of these are from the Middle Eocene Princeton Chert of British Columbia including, Soleredera rhizomorpha, Ethela sargantiana, and a coryphoid palm, Uhlia allenbyensis all of which are clearly distinct from the Appian Way monocot. Spadices of an aroid, Appaniospadix bogneri, recently described from Appian Way, show sclereid clusters similar to those seen in the new stem.  However, the inflorescence axis lacks the scattered bundles seen in the new stem, and we cannot link this reproductive structure to the stem at this time with our current level of knowledge of the anatomy.