Vegetative Growth of Eorhiza arnoldii Robison and Person from the Middle Eocene Princeton Chert Locality of British Columbia

Abstract

Anatomical studies of several thousand specimens of Eorhiza arnoldii Robison and Person rhizomes and their attached organs have added significantly to our knowledge of these Middle Eocene, semiaquatic dicotyledonous plants from the Princeton chert. Anatomical structure of Eorhiza was studied through serial sections on cellulose acetate peels. In order to establish the growth habit for these plants, individual axes were mapped as to their three-dimensional positions in the chert matrix. Plants grew from an extensive sympodial rhizome system similar to many living monocots and exhibited subopposite branching. Branches gave rise to rhizome sympodia or to branches bearing small scale-leaves. The architecture of Eorhizaconforms to the Tomlinson Model proposed by Halle, Oldeman, and Tomlinson. Leaves are ensiform, equitant, unifacial (isobilateral), and monocot-like with a large central lacuna. Rhizomes show typical dicot stelar anatomy. The presence of an aerenchymatous cortex and the plants' association with ...