PHYLOGENETIC RELATIONSHIPS AND TAXONOMIC STATUS OF THE PALEOENDEMIC FAGACEAE OF WESTERN NORTH AMERICA: RECOGNITION OF A NEW GENUS, NOTHOLITHOCARPUS PAUL S. MANOS Department of Biology, Duke University, Box 90338, Durham, NC 27708 pmanos@duke.edu CHARLES H. CANNON Department of Biological Sciences, Texas Tech University, Box 43131, Lubbock, TX 79409; Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Menglun, Mengla, Yunnan 666303, China chuck@xtbg.ac.cn SANG-HUN OH L. H. Bailey Hortorium, 412 Mann Library, Cornell University, Ithaca, NY 14853 so253@cornell.edu ABSTRACT We investigated the phylogenetic relationships and taxonomic status of the castaneoid component (Lithocarpus and Chrysolepis) of the family Fagaceae that is endemic to the California Floristic Province (CA-FP). Over 7800 basepairs of nuclear and chloroplast DNA were analyzed in 17 taxa representing the breadth of phylogenetic diversity in the family. The genus Lithocarpus, as currently defined, is clearly polyphyletic due to the inclusion of L. densiflorus. Here, we designate this taxon as a new genus, Notholithocarpus, which can be recognized morphologically by its relatively small, subprolate pollen. Notholithocarpus is more closely related to Quercus, Castanea, and Castanopsis; Chrysolepis was resolved as the sister group to Lithocarpus sensu stricto. These results indicate that Notholithocarpus does not possess true ‘flower cupules,’ which define Lithocarpus sensu stricto, but like the oaks, the single flower per cupule is derived through the abortion of lateral flowers within each cupule. Further study is required to confirm this characteristic. A formal taxonomic treatment is presented with new combinations. Key Words: California Floristic Province, Chrysolepis, Fagaceae, Lithocarpus, Notholithocarpus, phylogeny, sudden oak death, tanbark oak. The California Floristic Province (CA-FP) of western North America is rich in paleoendemic plant species that highlight the botanical legacy of the region and stimulate discussion on the affinities of many of these putatively isolated taxa (Stebbins and Major 1965; Raven and Axelrod 1978). Among these taxa are representatives of the largely tropical East Asian castaneoid sub- family of the Fagaceae: Chrysolepis Hjelmq. and Lithocarpus Blume. Both are morphologically similar to other broadleaf evergreen Fagaceae of eastern Asia, but their phylogenetic position within Fagaceae is either unresolved or has been put into question with recently available data. In this study, we address the relationships of the castaneoids of the CA-FP and discuss the implications of our findings in the context of taxonomy, cupule evolution, and biogeography. The two castaneoid taxa in question are well represented in several CA-FP communities (Bar- bour and Minnich 2000), and both express sufficient differentiation in habit and leaf morphol- ogy for the recognition of taxa at the subspecific- to species-level. The tanbark oak, Lithocarpus densi- florus var. densiflorus (Hook. & Arn.) Rehder, a tree that reaches 45 m, often occurs as a co- dominant in the redwood and mixed evergreen forests of the north coast ranges; its shrub form, L. densiflorus var. echinoides (R. Br. ter) Abrams is more common in open conifer forests and dry slopes of the northern interior CA-FP at higher elevations. The giant chinquapin, Chrysolepis chrysophylla (Douglas ex Hook.) Hjelmq., a tree potentially reaching 50 m, also occurs mostly in redwood and mixed evergreen forest. The bush chinquapin, Chrysolepis sempervirens (Kell.) Hjelmq., is more common at higher elevations as a low-growing shrub on rocky slopes under coniferous forests of the Sierra Nevada and in the isolated interior ranges of southern California. Taxonomic delimitation of the castaneoid genera is based largely on characters of the pistillate flower and cupule. The most important morphological characteristic for defining Chryso- lepis is a cupule with internal valves separating the fruits (Hjelmquist 1948). This condition is autapomorphic within Fagaceae, and the valves have been interpreted as vestiges of the branches MADRON ˜ O, Vol. 55, No. 3, pp. 181–190, 2008