Liquidambar, Altingia and Semiliquidambar comprise a distinctive clade that has previously been recognized as a subfamily of the Hamamelidaceae. The Altingiaceae shows a disjunct distribution in the Northern Hemisphere with Liquidambar from the temperate zone, and Altingia and Semiliquidambar in the tropical and subtropical regions. These arborescent genera have unisexual, capitate, globose-to-obconical woody infructescences composed of helically-arranged, biloculate capsules bearing relatively few viable, and many abortive seeds. Although these plants have been well known for some time, their taxonomic delimitation has recently been questioned. Our study of middle Miocene-aged, anatomically preserved infructescences from central Washington State, USA and Denmark provides the first evidence for internal structure of Neogene Liquidambar reproductive remains. We compare these fossils in detail to a comprehensive survey of extant relatives. Many previously undocumented features of infructescence structure, carpel and seed anatomy and micromorphology show that the Miocene forms are more similar to the eastern Asian Liquidambar acalycina and possibly Altingia and Semiliquidambar, than to the eastern North American L. styraciflua and the western Asian L. orientalis. Our study shows that many of the modern features of extant Altingiaceae were present in fossils from North America and Europe by the Miocene. By using anatomically preserved fossil reproductive remains, we have the opportunity to independently test hypotheses of phylogeny and biogeography that have been previously supported by isozyme and molecular studies.

Key words: Altingia, Altingiaceae, evolution and biogeography, fossil infructescences, Liquidambar, Miocene