Studies of Paleozoic Ferns: Tubicaulis stewartii Sp. Nov. and Evolutionary Trends in the Genus

Abstract

Eggert, Donald A. (Yale U., New Haven, Conn.) Studies of Paleozoic ferns: Tubicaulis stewartii sp. nov. and evolutionary trends in the genus. Amer. Jour. Bot. 46(8): 594–602. Illus. 1959.—Tubicaulis stewartii, a new species of the order Coenopteridales is described. The specimen was derived from the Upper Pennsylvanian of Berryville, Illinois, and is characterized by having a lacunar middle cortex, a well-developed integumentary system bearing uniseriate hairs, and xylem parenchyma organized into vertically anastomosing strands. In addition, multiseriate (somewhat transitional to reticulate) bordered pitting is present in the petiolar metaxylem elements, while those of the stem stele are multiseriate scalariform. The habit is intermediate between that of a form such as Osmunda and a tree fern, having an upright tapering stem which gives off prominently decurrent petioles in a 2/5 divergence. A reinvestigation of the type specimen of the most closely allied species, T. multiscalariformis, of Upper-Middle Pennsylvanian age, has shown that it has similar features in the cortex, metaxylem, and integumentary layers. Tubicaulis multiscalariformis and T. stewartii form a distinct group in the 6 species now known, whose evolution has most likely involved the retention of a more primitive form of pitting (multiseriate scalariform) with parenchymatization of the xylem. The remaining species of the genus have not developed xylem parenchyma but have developed circular bordered pitting. The relationships of the genus to other genera in the Coenopteridales remain obscure.