male catkin © J.R.Manhart

Salix nigra APMRU

Salix nigra APMRU

Salix (willow) pollen is one of the most common and recognizable pollen grains recovered from aquatic sediments. Unfortunately, the small, tricolporate, reticulate grains resemble those of other plants.

Salix (willow) includes over 300 species, found mostly in the arctic to temperate northern hemisphere. None of the Salicaceae are native to Australia. The leaves are generally simple, alternate and narrow. The female and male flowers are on different stems. The seeds are small (< 2 mm) with a white tuft (coma). They only germinate in saturated soil, but willows proliferate asexually through underground stems. The plant form ranges from dwarf shrubs (tundra) to tall (20 m) streamside trees.

Pollen light micrograph:
Generally small, 20 - 25 µm, prolate, reticulate pollen grains, with a pronounced margo. The reticulation (both muri and lumina) decreases in size near the furrow, often producing a psilate margo parallel to the furrow. The muri of the reticulation varies from very sharp to broadly rounded, and the lumina generally decrease in size at the poles.

Pollen scanning electron micrograph (SEM)
The APMRU micrograph clearly displays the distinctive margo, and the football (rugby!) shape of the willow grain.

Production and Dispersal:
Willows are both wind and insect pollinated, even within single species. Their pollen production and dispersal are moderate.


Fossil Occurrence:
The primitive morphology of the plants suggests antiquity of the willows, however, the earliest pollen (Japan) is of Eocene age, and its pollen is not common in North America until the Eocene (Tsudy and Scott, 1969).

  • Adams, R. J. and J. K. Morton 1972 - 1979.
    An atlas of pollen of the trees and shrubs of eastern Canada and the adjacent United States. Parts 1 - 4.
    Very nice treatment in part 1, pp. 22-27 of several species (SEMs).
  • Tralau, H., Zagwijn, W.H. 1962.
    Fossil Salix polaris Wahlbg. in the Netherlands. Acta Botanica neerlandica 11: 425-427.
  • Rowley, J.R. and Erdtman, G. 1967.
    Sporoderm in Populus and Salix. Grana Palynologica 7: 517-567.
  • Tschudy, R.H. and Scott, R.A. 1969.
    Aspects of palynology. John Wiley & Sons, New York. 510 p.

Owen Davis 9/01