RILEY, MICHAEL G.* AND RUTH A. STOCKEY. Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada, T6G 2E9. - A new aquatic angiosperm with a floating rosette of leaves from the St. Mary River Formation of southern Alberta.
Three hundred specimens of a new aquatic angiosperm have been
excavated from the Upper Cretaceous deposits of the St. Mary River
Formaton (Maastrichtian) of southern Alberta, Canada. Plants are
compression/impressions and are represented primarily by isolated
leaflets found in grey siltstones and fine-grained sandstones. These
sediments probably represent a sudden overbank flood. The remains of
13 complete or partial rosettes of this dicot have been identified in
the grey siltstones. Growth habit is similar to that described for
Quereuxia (=Trapago) angulata from the same
locality. The leaves of the new plant, however, are more than twice
the size of those of Q. angulata and the largest rosettes
measure at least 16 cm in diameter. Leaves are opposite, simple at
the first two nodes from the apex, and compound with three leaflets
for at least four nodes below. Blades of leaves or leaflets are
symmetrical, obovate, microphyllous with obtuse to rounded apices and
bases. The margin is unlobed and crenate. Five to seven primary
veins enter from the petiole/petiolule exhibiting reticulate
actinodromous to pinnate, craspedodromous branching. Primary veins
are thicker near the base and weaker near the apex and show
deflections near the leaflet tip. Secondary veins branch
dichotomously and thin toward the margin. Tertiary veins are random
reticulate with quaternaries forming irregular areolae. Leaves were
probably aerenchymatous and fleshy with the abaxial epidermis being
preserved on several specimens. Teeth appear to have been
chloranthoid or rosoid. Rosettes are attached to a vertical axis, the
largest being at least 11 cm in length. The rosettes were probably
floating on the surface on a shallow pond or oxbow lake. These plants
are found in the same deposits as Quereuxia angulata and the
two species shared the same habitat.
Key words: Alberta, aquatic, dicot, Quereuxia, rosette, Upper Cretaceous