ITOPSIDEMA, A NEW GENUS OF THE OSMUNDACEAE FROM THE TRIASSIC OF ARIZONA

Abstract

Daugherty, Lyman H. (San Jose State College, San Jose, Calif.) Itopsidema, a new genus of the Osmundaceae from the Triassic of Arizona. Amer. Jour. Bot 47(9): 771–777. Illus. 1960.—Itopsidema vancleavei, a new genus and species of the family Osmundaceae, is described. The specimen consists of several segments of an arborescent stem obtained from the Upper Triassic of the Petrified Forest National Monument near Holbrook, Arizona. The surfaces on 2 of the segments are covered by adventitious roots and the remaining segments are covered by leaf bases. The fronds are spirally arranged and have an 8/21 phyllotaxy. The cortex of the stem, which contains numerous leaf traces and adventitious roots, consists of parenchyma with cell walls of medium thickness. The leaf traces are oblong to crescent‐shaped in the inner cortex and horseshoe‐shaped in the outer cortex. The base of the petiole contains a single, large vascular bundle and is covered by multicelled, glandular spines. The adventitious roots originate on the abaxial side of the leaf traces in the region of the inner cortex. The center of the stem is occupied by an ectophloic, mesarch siphonostele without leaf gaps. The pith is composed of firm‐walled parenchyma cells which have isolated tracheids with reticulate pitting scattered among them. These tracheids are so rare the pith cannot be considered a “mixed pith.” The relationship and morphological significance of Itopsidema with respect to other members of the Osmundaceae are briefly discussed.