Taxonomy of Flowering Plants - LECTURE NOTES - Spring, 1998
Hugh D. Wilson - rm. 306, Butler Hall
9 March 1998
The Dilleniidae
Family Overview - The Salicales

Salicaceae - the Willow Family

Diversity:  Only two genera, willows (Salix - ca. 300 species) and poplars (Populus - ca. 40 species) but, as was the case with taxa of the Hamamelidae, the relatively small number of species includes many with a wide distribution and, as a result, plants of the family - all woody (shrubs or trees) are conspicuous elements and frequently encountered.  

Distribution:  Throughout temperate parts of the World with maximum diversity toward the north and strong ecological preference to habitats associated with water.  In our flora, taxa of both genera will be found beside ponds and along streams and rivers.

Floral structure:

 
 
Significant features:  Floral structure of the Salicaceae is an expression of extreme reduction.  The pistillate flower is represented by only a single, compound pistil and the staminate flower is, in Salix species, just two stamens.  These imperfect flowers are produced in catkins and most species of the family are dioecious.  While the reproductive adaptive syndrome of the Salicaceae mimics that of the Hamamelidae, there is general agreement that this similarity is not based on common ancestry and most classification systems place this family in a position well removed from families of the Hamamelidae.  This points out the importance of the gynoecium in that the primary structural difference between this family and the other 'amentiferous' flowering plants is the capsular fruit.  As indicated by the local name for our most common poplar - 'cottonwood' - seeds emerging from capsules of the Salicaceae are comose (with a tuft of trichomes) and, as a result, all reproductive events - pollination, fertilization and dispersal of the product - are wind-mediated in this family.
  

 The single representative of Salix in our local flora - S. nigra:
 

Staminate catkin at anthesis
Pistillate catkin at anthesis
Pistillate catkin with fruit and comose seeds
 
  Staminate catkin of Salix with dark bract subtending each flower
 
 

    Populus nigra - overview -  from Kohler's Medicinal Plants
 
  The aspen (Populus tremuloides) is a rhizomatous woody perennial.  A single plant can therefore produce many shoots and a 'stand' of aspen often represents a single plant.  The relatively recent capability to employ molecular markers to identify individuals has allowed large 'clones' to be defined and, given the growth rate for this plants, some of the larger aspen clones might be the oldest living individuals.
 
 
 

More information on the Salicaceae

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