title: Alnus subgenus Alnus in the Eocene of western North America based on leaves, associated catkins, pollen, and fruits.
abstract: OBJECTIVE
  The fossil record of alder (Alnus) is well known in the Cenozoic deposits throughout the northern hemisphere, based on numerous reports of the distinctive pollen, cone-like infructescences, staminate inflorescences, and leaves. However, our understanding of the systematic position of these fossils relative to the modern phylogeny of the genus has been limited because most fossils were described from only one organ.
  
  
  METHODS
  We examined well-preserved leaves and associated fruiting and staminate catkins from the middle Eocene, Clarno Formation, Oregon, USA by stereomicroscopy. In situ and dispersed pollen were cleaned with HF and acetolized for light and scanning electron microscopy.
  
  
  RESULTS
  We reconstructed a new extinct species based on multiple organs and discuss significant phytogeographic and phylogenetic implications for Alnus. Alnus clarnoensis sp. nov. is described based on serrate leaves with 1-4 small teeth between each primary tooth, associated cone-like fruiting catkins with fruits in situ, and associated slender pollen catkins bearing in situ 3- to 6-pored pollen with arci between the pores. Combined investigations of each organ indicate that they probably derive from the same species and can be confidently attributed to subgenus Alnus Furlow based on leaf architecture and pollen pore number frequency.
  
  
  CONCLUSIONS
  The Clarno fossils are most similar to the extant North American species of subgenus Alnus rather than to those from Asia and Europe, indicating that this modern subgenus was already distinct by the middle Eocene and that the intercontinental migration likely occurred earlier.
authors.affiliation: State Key Laboratory of Biocontrol and Guangdong Key Laboratory of Plant Resources, School of Life Sciences, Sun Yat-sen University, Guangzhou 510275, China Florida Museum of Natural History, University of Florida, Gainesville, Florida 32611-7800 USA.
authors.forename: Xiaoyan
authors.initials: X
authors.lastname: Liu
authors.affiliation: Florida Museum of Natural History, University of Florida, Gainesville, Florida 32611-7800 USA.
authors.forename: Steven R
authors.initials: SR
authors.lastname: Manchester
authors.affiliation: State Key Laboratory of Biocontrol and Guangdong Key Laboratory of Plant Resources, School of Life Sciences, Sun Yat-sen University, Guangzhou 510275, China.
authors.forename: Jianhua
authors.initials: J
authors.lastname: Jin
mesh_terms: D029661:Alnus / Q000033:anatomy & histology / Q000145:classification*; D005580:Fossils; D005638:Fruit / Q000033:anatomy & histology / Q000145:classification; D009922:Oregon; D010802:Phylogeny; D018515:Plant Leaves / Q000033:anatomy & histology / Q000145:classification; D011058:Pollen / Q000033:anatomy & histology / Q000145:classification
keywords: Alnus; Betulaceae; Clarno Formation; Oregon; biogeography; fossil plant; middle Eocene