Tracing the Cenozoic History of Roses (Rosaceae: Rosa) in North America Based on Fossil Foliage and Fruiting Remains.

Premise of research. Roses have been horticulturally important for centuries, but their biogeographic history has remained largely unresolved. Fossil occurrences indicate that the genus was present in North America by the late Eocene and in Europe and Asia by the Oligocene. Given the age and importance of this genus, it is desirable to update as new fossils are uncovered and technologies advance. Methodology. Specimens preserved in lacustrine shales were studied by reflected light microscopy and micro–computed tomography scanning. Pivotal results. The fossil record of roses is summarized based on stipulate compound leaves and fruiting remains from western North America. Diagnostic characters of foliage and fruiting receptacles confirm identifications of Rosa from late Eocene, Oligocene, and Miocene sites in western North America and distinguish them from European and Asian fossil species. Rose hip species were found to vary in body shape and length of the apical neck. The hips from Colorado and Montana lacked prickles, while those from Oregon bore small prickles on the pedicel. Conclusions. A single largely uniform foliage type, R. hilliae Lesquereux, is recognized in the late Eocene and early Oligocene of western North America, while fruiting remains allow discrimination of two species, R. ruskiniana Cockerell from the late Eocene and early Oligocene of Colorado and Montana and R. mariae sp. nov. from the early Oligocene of Oregon. Another new species, R. packardae sp. nov., is recognized based on hips from the middle Miocene of Oregon. Reproductive structures were distinguished on the basis of differences in calyx lobing, receptacle shape, and epidermal projections on the pedicel. Among extant Rosa species, hip shapes are most commonly globose or subglobose, whereas North American fossils mostly display elliptical or urceolate hips. Urceolate hips in extant species are found in the subgenus Rosa , sections Cinnamomeae or Canieae, indicating potential infrageneric affinities for these fossils. [ABSTRACT FROM AUTHOR]