STUDIES OF PALEOZOIC FERNS: TUBICAULIS STEWARTII SP. NOV. AND EVOLUTIONARY TRENDS IN THE GENUS

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. THE ORDER Coenopteridales is composed of Paleozoic fern-like plants not referable to modern families. These poorly understood plants make up a highly artificial group showing definitely fernlike features, but generally differing from extant ferns in frond symmetry, type of stele, petiole trace symmetry, and in sporangial morphology and position. Supposed relationships in the order are based almost entirely upon anatomical characteristics of stem and petiole parts, for in most instances neither the fructification nor the complete frond is known. Relatively small anatomical differences have been emphasized in the separation of the families and genera. This is in contrast to the classification of living ferns where sporangial morphology is the most important single taxonomic feature. The Coenopteridales possess many recognizably primitive features, such as protostelic vascular systems and sporangia borne on stems, as well as more advanced characters, such as medullated steles and synangiate fructifications. Classification of the group is largely a matter of convenience and expediency, in most instances, although there are some genera, such as Botryopteris, that appear to be roughly equivalent to genera as they are defined in living forms. One of the most recent taxonomic treatments is the admittedly artificial one of Morgan and Delevoryas (1954), in 'Received for publication February 20, 1959. The author wishes to thank Dr. T. Delevoryas, Dept. of Botany, Yale University, for his advice, constructive criticism, and encouragement during the course of the present investigation. His aid in preparing the photographs also is gratefully acknowledged. The species was named in honor of the collector of the type specimen, Dr. W. N. Stewart, Dept. of Botany, University of Illinois, who donated the specimen to our laboratory for study. which 4 families are delimited: the Stauropteridaceae, Botryopteridaceae, Zygopteridaceae, and the Anachoropteridaceae. The present paper deals with the genus Tubicaulis, placed in the family Anachoropteridaceae by the above authors. Discovery of the new species described in this paper has led to a reinvestigation of the type material of the allied species, T. multiscalariformis (Delevoryas and Morgan, 1952). Features have been found in that species which closely ally it to the newly described one, although the 2 are distinct. DESCRIPTION OF THE NEW SPECIMEN.-The specimen is Upper Pennsylvanian in age and was found in a coal ball from Lawrence County, near Berryville, Illinois. It consisted of 2 pieces of stem, each having attached petioles. One piece includes apical portions of the plant while the other includes more basal parts. The 2 pieces in all likelihood are from the same individual. A general scheme of the orientation, and relative size of the 2 specimens is shown in fig. 1. The preservation of the new specimen is the most nearly perfect yet reported for the genus, so that one can determine details of structure seemingly lost in previously described forms. General features.-The species apparently had an upright habit with elongate tapering stems and closely appressed, relatively large petioles. The habit may be considered as intermediate between the condition in Osmunda, in which closely spaced nodes are present, and that in tree ferns, where variously spaced leaves arise from an upright stem. Stem.-Because of the attached petiole bases, the stem has a lobed appearance (fig. 2) and is variable in diameter. Apically, the stem appears somewhat elliptical in outline when viewed in cross section (fig. 5), but sections made at lower levels are more