INVESTIGATIONS OF NORTH AMERICAN CYCADEOIDS: MONANTHESIA

DELEVORYAS, THEODORE. (Yale U., New Haven, Conn.) Investigations of North American cycadeoids: Monanthesia. Amer. Jour. Bot. 46(9) :657-666. Illus. 1959.-A study of the cycadeoid trunks from the Upper Cretaceous Mesaverde formation of northwestern New Mexico, which arr in the collections of the Peabody Museum of Natural History, Yale University, has been completed. These plants had columnar trunks with persistent leaf bases and a cone in the axil of every leaf. The vascular supply of the cone is derived from the fusion of two cortical bundles which arise from two leaf traces, neither of which supplies the subtending leaf. Enough difference appears to exist between these forms and Cycadeoidea to warrant a separate generic designation. Monanthesia is the generic name used, and the single species, M. magnifica, is considered to include all the stems from the New Mexico localities. The pattern of vascularization of cones seems to suggest that they are foliar structures and that Monanthesia is probably a more advanced form than Cycadeoidea. IN THE Carnegie Institution Year Book No. 27 for 1927-28, the late Professor G. R. Wieland reported on cycadeoid collections made in the San Juan Basin in northwestern New Mexico from Upper Cretaceous (Mesaverde) deposits. Most of the trunks originated in the Navajo Indian Reservation in the vicinity of the Chuska Mountains. The trunks collected by Wieland during 1928-29 are part of the extensive cycadeoid collection at the Peabody Museum of Natural History, Yale University. In general, these fossil specimens are not ovoid or spherical, but columnar, and are of interest because of the presence of a fructification, or cone, in the axil of just about every leaf (fig. 1, 2). In the same report, Wieland listed 6 previously described species of Cycadeoidea which he thought had a similar habit. These are: C. dartoni, C. fisherae, C. stantoni, C. masseiana, C. nigra, and C. niobrarensis. It was in this paper that Wieland suggested that these 6 species of cycadeoids, and the newly found New Mexico specimens, might be given a new generic name. At that time he proposed the name Navajoia. However, because the name Navajoia does not meet the requirements for valid publication in Article 36 of the 1956 edition of the International Code of Botanical Nomenclature, it is a nomen nudun. Furthermore, no formal transfer of the 6 Cycadeoidea species was made. No mention of the name Navajoia was made in subsequent papers by Wieland; in fact, he continued to refer the 6 previously named species to Received for publication March 31, 1959. This work was supported in part by a grant from the National Science Foundation. The author wishes to extend grateful appreciation to Professor Carl 0. Dunbar, Emeritus Director of Peabody Museum of Natural History, Yale University, for his cooperation and for permission to work on the cycadeoid collection in that institution. The author also acknowledges, with thanks, the advice of Professor John R. Reeder, Department of Botany, Yale University, on certain taxonomic problems. Cycadeoidea, in spite of his having proposed the name Navajoia for them earlier. In 1934, Wieland introduced the name Monanthesia for the New Mexico specimens. In that paper there is a photograph of a tangential section of the armor of a specimen (text fig. 20) with a brief description of it under the combination M. magnifica. If Monanthesia had been instituted by Wieland as a monotypic genus, this combined generic and specific description would validate the genus according to provisions of Articles 36 and 41 of the Code. However, it is obvious that he had intended to include more than 1 species in Monanthesia because in the same paper (Wieland, 1934; p. 94, 110) Wieland referred to a second species, M. blanca, and included descriptive remarks concerning that species. Thus, the descriptio ganerico-specifica of M. magnifica does not validate the genus Monanthesia. The name Monanthesia was used by Wieland in several subsequent papers (1935, 1936a, 1936b, 1937, 1941), but in none of these is there an unquestionable validation of the genus. Because the New Mexico group of cycadeoids was the least investigated in the Peabody Museum collection, the author initiated a thorough study of the group. An attempt was made to determine whether the New Mexico complex was truly distinct, or whether they were close enough to Cycadeoidea to be included in that genus. In addition, a study of the vascularization of this interesting group was made with the purpose of learning more of the anatomy and evolution of the cycadeoids. GENERAL STRUCTURE.-The columnar trunks of the Mesaverde cycadeoids may reach 70 cm. or more in height, with a diameter of 50 cm. (fig. 1). Seldom are the complete trunks found intact. Many of them are flattened, and the matrix of most of them is coarse, yielding poor structural details. Another difficulty encountered is the fact that the cone peduncles are long and slender, and quite