Pollen morphology of the three subgenera of Alnus

The three subgenera of alder (Alnusroman Clethropsis and Alnobetula) are taxonomically distinctive, but how does their pollen match up with their gross morphology? This study links pollen characters with the taxonomic divisions of the genus alder based on nrDNA ITS sequence data. The value of the study is in the breadth of the taxonomic coverage of the three subgenera, as the samples per species only range from 1 to 6. From 29 Alnus species, the authors studied pollen from 59 modern reference collections (prepared by acetolysis) and recorded the number and type of apertures (pores), thickness of the arci, pollen size and polar arci. Tallies of the number of pores on the pollen grains in a reference collection typically have a range of ± 1 or 2. Exceptions are presumed hybrid collections in Alnus rugosa with a range of ± 5, which have malformed pollen cells suggesting infertility. The presumed hybrids show a greater range of both pore number and size of pollen grains. The dominant pore number is a key feature that separates the subgenus Alnobetula (= Alnaster) from the other two subgenera by consistently having predominantly 5-, 6- or 7-pored pollen grains, while all other Alnus taxa sampled have pollen with predominantly 4- or 5-pored pollen. The dominant pore number is a consistent feature within the subgenus Alnobetula (10 species), but is inconsistent in 3 out of 16 species of the subgenus Alnus and within the subgenus Clethropsis (3 species). Thickenings of the pore lip, aspidate (protruding) and vestibulate pores are important features of Alnus pollen on a species level. Alnus-like pollen morphology occurs occasionally in certain other betulaceous genera (Betula and Carpinus). Differences in character or thickness of arci (band-like thickenings on the pollen wall between pores) tend to be somewhat consistent within a species and vary within subgenera. Two Alnobetula species in the Alnus viridis complex (Alnus crispa and Alnus sinuata) have arci that are weakly developed or appear as simple folds; walls are fragile and pores are typically less aspidate. Pollen sizes in different species overlap greatly, may be partly influenced by processing methods and do not seem to be generally helpful in characterizing species. Circular doughnut-shaped arci thickenings on the polar area of pollen grains are a common feature (16–40%) in two closely related East Asian taxa of subgenus Alnobetula with large pollen (‘Clade A’: Alnus firma and Alnus sieboldii). These ‘Clade A’ features have been reported from Miocene collections of Alnus pollen from Alaska, and support megafossil evidence in determining the biogeography of this group along the Pacific Rim in the Neogene. The Miocene appearance of subgenus Alnobetula megafossils in both Alaska and Japan can only have occurred via a Bering Land Bridge. This relation is now confirmed by Reinink-Smith's Miocene ‘Clade-A-type’ pollen data of Alaska. These taxa had Pacific Rim distributions, similar fruiting carposamaras and now correspond to a DNA ITS subgroup within Alnobetula. Depending on the geographic location with limited number of local alder species, certain Holocene identifications are possible based on pore structure and arci thickness, e.g. the Alnus crispa-type in eastern Canada and the Alnus sinuata-type in the Pacific northwest.Fil: Leopold, Estella B.. University of Washington; Estados UnidosFil: Birkebak, Joshua. University of Washington; Estados UnidosFil: Reinink-Smith, Linda. University of Washington; Estados UnidosFil: Jayachandar, Anitha P.. University of Washington; Estados UnidosFil: Narvaez, Paula Liliana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Zaborac-Reed, Stephanie. University of Washington; Estados Unido

Determining the Paleoclimate and Elevation of the Late Eocene Florissant Flora: Support from the Coexistence Approach

Published estimates on the paleoclimate of the Florissant fossil beds site of Colorado (34.1 Ma) have led to extremely different estimates of paleoelevation. The purpose of this paper is to review the paleoclimate methods used, and to add the Coexistence Approach (CA) method to estimate paleotemperature for the Florissant site. The basis of the CA method is the dependence on overlapping climatic requirements for different taxa in the flora and their nearest living relatives. These relationships tie the fossil identities to the actual plant habitats and climatic requirements of close relatives. Based on the CA method, we conclude that the mean annual temperature ranged between 14.3° C and 18.2° C. These results support the conclusions offered by several other studies that the Florissant was a warm-temperate to subtropical flora, and are consistent with recent conclusions by structural geologists as well as other studies indicating that the Florissant site was deposited at a relatively low elevation, probably between 1 to 1.5 km.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author