STUDIES IN THE QUERCUS UNDULATA COMPLEX I. A PRELIMINARY STATEMENT

TUCKER, JOHN M. (U. California, Davis.) Studies in the Quercus undulata complex. I. A preliminary statement. Amer. Jour. Bot. 48(3): 202-208. Illus. 1961.-The taxonomic history of Quercus itndildata, a highly variable, problematic complex of the Southwest, is discussed. Conservatively treated as a single species, it comprises a wide range of forms which at one extreme approach Q. gambelii morphologically, and, at the other, Q. grisea, Q. turbinella, and other species. The postulate was made that Q. undilata had arisen through hybridization between these very different oaks. Field observations and preliminary study of numerous population samples confirm this postulate. (Detailed morphological analyses are in progress.) Seven species have apparently been involved-Q. gambelii (the "common denominator" of the complex) has hybridized in different parts of its range with one or another of the following: Q. arizonica, Q. turbinella, Q. havardii, Q. muehlenbergii, Q. mohriana, and Q. grisea. The latter 6 species are discussed individually, and the extent to which each contributes to the complex, and the area in which this occurs, are indicated. DURING the century and more that has passed since its naming, Quercus itndulata Torr. has been one of the most problematic oaks, taxonomically, in the western United States. On the one hand, it has been treated as a single polymorphic species; on the other, as an aggregate of many species, but rarelyuntil recent years-in a fashion satisfactory to the field taxonomist. Briefly, its taxonomic history is as follows. The name is based on a collection by Edwin P. James, naturalist with an expedition to the Rocky Mountains in 1819-1820, under the command of Major S. H. Long, U. S. Topographic Engineers. The type locality given by Torrey was: "sources of the Canadian [River], and the Rocky Mountains" (1828, p. 248). Nearly 50 years after its naming, and after a number of other species had been described from the Southwest, George Engelmann published a memoir on the oaks of the United States (1876). Engelmann's observations on the interrelationships of several white oaks of the Southwest, including Q. undulata, went directly to the crux of the problem, but his conclusions laid the groundwork for subsequent taxonomic confusion. Citing an area on the Arkansas River near Can-on City, Colorado, as the "classical locality" of "the common Rocky Mountain scrub oak" (Q. gambelii Nutt.), he ob1Received for publication June 17, 1960. Field work for this study was carried out during 1955-56, the Dept. of Biology, University of New Mexico, Albuquerque, serving as a base of operations. Thanks are due Prof. E. F. Castetter, then Chairman of the Department, for assistance and provision of facilities. Grateful acknowledgment is made to the John Simon Guggenheim Memorial Foundation for the fellowship which made this study possible; also to the curators of the herbaria at the following institutions for the loan of specimens: University of Arizona, Arnold Arboretum, Missouri Botanical Garden, University of Nevada, New York Botanical Garden, University of Oklahoma, Southern Methodist University, and the United States National Museum. served how, within a small localized area, the latter occurred with a number of other well-marked forms, each different from the rest. Several of these (Q. undulata, among others) had long been known as distinct species. The presence of numerous intermediate forms, however, clearly united them all, in Engelmann's view, "as forms of one single extremely polymorphous species" but, Engelmann continued in perplexity, "If one oak behaves thus, why not others? Thrown into a sea of doubt, what can guide us to a correct knowledge?" Quercus undulata was the name he applied to the complex as a whole (since this was the earliest name to be applied to any of the oaks involved), the other forms being treated as varieties of it. However, in addition to the various forms actually present in the vicinity of Can-on City, Engelmann also included under Q. undulata, at least tentatively, other oaks of the Southwest which do not occur in Colorado and which are not closely connected with Q. gainbelii or the undulata complex as it is now known, namely, Q. drummondii Lielbm., of central Texas, and Q. oblongifolia Torr. of southern Arizona (Engelmann, 1876, p. 382). Later, he added Q. sinuata var. breviloba (Torr.) C. H. Mull. (as var. breviloba of Q. undulata), another oak of central Texas, but excluded Q. oblongifolia (1877,pp. 392393). Engelmann's unduly conservative classification of these white oaks was paralleled, in large part, by the treatment of Sargent (1895), which differed mainly in maintaining Q. gambelii and Q. utndulata as distinct species. In retrospect, Sargent's treatment of the latter complex is clearly unsatisfactory, although it must be acknowledged that we have vastly more knowledge about the oaks of the Southwest today than he had in the early 1890's. It was probably inevitable that a reaction should come about before long, and come about it did! In 1901