Alnus (Betulaceae)

Alnus tenuifolia
Utah State Trees N. Utah

Alnus rugosa
U.Berkeley San Francisco Estuary

Provincial Mus. Alberta

Trees and shrubs with oval (2-5 cm) toothed leaves, generally rough bark. Reproduction by woody female and male catkins, seeds winged 2 mm. Temperate to alpine, Northern Hemisphere. Many species are riparian, others are understory species.

Pollen light micrograph:
Pollen oblate, 20 - 30 µ.m., stephanoporate (4 - 5 pores in equatorial plane) with distinctive lines of thickening (arci) joining the pores in both hemispheres. Surface scabrate to rugulate. Arci are external and internal.

Pollen scanning electron micrograph (SEM)
Arci are not evident on the grain shown above, but are evident in the sem by Martin and Drew.

Production and Dispersal:
Alders are wind pollinated, so production and dispersal are very good. Alder pollen is common. In the Pacific Northwest, alder is common in canopy openings of the coniferous forest, and was abundant during the mid-Holocene when the forest became open.

Well preserved.

Fossil Occurrence:
Cretaceous (?). Paleocene macrofossils in northern hermisphere. Common in Miocene (20 Ma) floras of western U.S.A.

    Elsik, W.C. 1966
    Degradation of Arci in a Fossil Alnus Pollen Grain. Nature, 209:825

    Takeoka, M. 1963.
    On the fine structure of the pollen walls in some Scandinavian Betulaceae Grana Palynologica 4: 161-188


Owen K. Davis 05/00