LITTLE, STEFAN A.* AND RUTH A. STOCKEY. Department of Biological Sciences, University of Alberta Edmonton, AB T6G 2E5 Canada. - Reconstructing aquatic angiosperms from the Middle Eocene Princeton chert : Decodon allenbyensis .
Aquatic Lythraceae remains were first recognized in the Princeton
chert by Cevallos-Ferriz and Stockey in 1988 with the description of
fruits and seeds of Decodon allenbyensis . Recently large
numbers of roots, stems and leaves have been identified along with the
fruit and seed remains from layer #43 in the chert. Fossils come from
the Allenby Formation (Middle Eocene) near Princeton, BC. Specimens
of the vegetative remains thought to belong to D. allenbyensis
were studied using the cellulose acetate peel technique in an
attempt to reconstruct the whole plant. Roots and stems show diffuse
porous wood with vessels that are solitary or in radial multiples of
two to five with numerous tyloses. Heterogenous rays vary from one to
at least five cells wide. Secondary phloem with clusters of
thick-walled fibers is preserved in some axes. Most of the roots and
some stems show distinctive concentric layers of thin walled lacunate
phellem, characteristic of submerged aquatics. Tissue of this type
has been described in Ammannia L., Lythrum L. and
Decodon verticillatus L. (Ell.) of Lythraceae. Leaves, roots,
stems, seeds and inflorescence axes of D. verticillatus have
been studied using paraffin techniques and scanning electron
microscopy and were closely compared to these remains in the chert.
Anatomy of D. allenbyensis suggests that these plants were
growing under submerged conditions with fluctuating water levels at
the edge of a shallow water system.
Key words: Decodon , Lythrum , Aquatic plants, Eocene, Lythraceae