Landscape Plants

Oregon Master Gardener Training – Woody Plant Identification

What should you expect from this particular training?

         It is estimated that there are some 352,000 flowering plant species (angiosperms) and nearly 1,000 gymnosperms(conifers, cycads, ginkgo, etc.).  To learn to identify that much material is a life’s work or, more likely, several lives.

• If we skip over the herbaceous plants (i.e., geraniums, petunias, columbine, etc.) we can greatly reduce the number of plants to be concerned about.  And this is what I do.  I only deal with woody ("macho") plants (trees, shrubs and woody vines).


• But still there are a lot of woody plants.  There are probably over 100,000 tree species; I don’t know the number of woody shrub and vine species.  Is it possible to lean that many woody plants?

What might be some strategies to recognize and name woody plants

• One could decide to only learn the woody plants native to Oregon.  This might be good place to start since this is a manageable number.  The Manual of Oregon Trees and Shrubs (305 p), by Ed Jensen and others, is used for native tree and shrub identification in the College of Forestry at Oregon State University.   With this little field book we can get an idea of the numbers of species in some of the common categories (genera) of trees and shrubs.

• This of course is not the total number of woody plant species in Oregon.  In the Oregon State University Landscape Plants website there are about 130 woody species listed in the Native and Naturalized Woody Plants of Oregon. This list is incomplete….so let’s say about 150-200. One could learn this number of plants in a relatively short time.

• Now let’s say you want to move beyond Oregon’s woody natives and include the common woody landscape plants. If one adds cultivated woody plants to the list, the number of “different” kinds of plants increases dramatically.   Woody landscape plants would not only include some Oregon woody plants, but plants native and/or selected from around the world. Here are a few examples of the total number of species of several kinds of woody plants:
   

  Genus	Oregon Natives	Approx. Total   No. of Species	"Manual of  Woody Landscape Plants"  (2009)
  			Approx. No. Species	Approx. No. Selections
  Pine (Pinus)	8	110	45	90
  Ash (Fraxinus)	1	60	11	60
  Dogwood (Cornus)	3	45	28	300
  Maple (Acer)	4	130	55	290
  Oak (Quercus)	3	600	15	50
  Cotoneaster	0	70	16	40
  Viburnum	2	150	60	230
  Vaccinium	4	450	14	170

  
  For various reasons, not all of these species are suitable as landscape plants, especially in the Pacific Northwest.   But still the number of woody landscape plant species is rather large.  In the highly regarded and comprehensive Manual of Woody Landscape Plants by Michael Dirr, the approximate numbers of species that are described or mentioned in each of several genera are shown above.  Also given is the number of plant selections that Dirr listed for each genus.
   
• A plant selection is a plant that has been "selected" or developed from a population because it displays one or more desirable characteristics.   If such a plant is of potential commercial value it is given a specific cultivar or trademark name (e.g., 'Crimson Glory', or Red Sunset®).  Some woody plant species are very popular in commerce and are represented by a large number of selections.   For example, Dirr describes nearly 40 selections of Norway Maple (Acer platanoides) and over 70 selections of Red Maple (Acer rubrum).  Although some cultivars within a given woody species are so unique they are easy to identify, for those just starting to identify woody plants it is probably best to limit their attention to only a few selections.


• An enjoyable way to lean to recognize woody landscape plants in your area or region is to frequently visit nurseries and botanical gardens or other locations where plants are labeled.  Make a list of plants you see and then try to identify them at some later time.  Books, magazines and especially websites with pictures are a wonderful help in leaning to identify woody plants.  Using this approach one can accurately recognize and name a large number of plants without much botanical training.

• A more systematic method to identify plants is by using so-called keys, most often dichotomous keys. This type of key that offers at least two alternatives at each step (a dichotomy).  For example:
  
     1a Leaves simple
           2a  Leaves alternate
           2aa  Leaves opposite
     1b Leaves compound
           2b  Leaves alternate
           2bb  Leaves opposite
  
  Dichotomous keys are excellent tools to help in plant identification, but they often use precise botanical terms, and if these are misinterpreted it is easy to get off on the wrong track.  Such keys are probably best for identifying native plants growing in a limited region (e.g., western Oregon).  They are of less value when trying to identifying landscape plants, for these consist of species from all over the word and many selections developed from these species.  Below are a few references which contain dichotomous keys for woody plants.  Many more plant keys are available on the internet.
  •  Muenscher’s Keys to Woody Plants: An Expanded Guide to Native and Cultivated Species.   Edward A. Cope, 2001. Cornell University Press.  A fairly comprehensive dichotomous key, but it is best suited to eastern North America; it does not often included plants common to the Pacific Northwest.
  • Manual of Oregon Trees and Shrubs.  E. C. Jensen, W. R. Randall, R. F Keniston, and D. N. Bever. (10th Ed.), 2012, John Bell and Associates, Corvallis, Oregon.  A small field book useful for identifying trees and shrubs native to Oregon.
  • Trees to Know in Oregon.  E.C. Jensen, 7th Ed., 2012, Oregon State Univ. Extension.   The dichotomous key is also available   on line.
  • Shrubs to Know in Pacific Northwest Forests  E.C. Jensen, 2013, Oregon State Univ. Extension
  • Dichotomous Keys: here are two dichotomous keys on the web
    • Dichotomous Key to Plant Families    This website can be used to identify the family of a given plant, which can be a big step in making an identification.   The site is limited to plants in New England. 

    • Keys from the Arboretum Wespelaar in Wespelaar, Belgium   Select Identification keys and illustrations from the list on the left.

  • Another approach is the use searchable woody plant databases.  In this case the user usually selects items from lists of plant characteristics that are observed in the unknown plants (e.g., leaf shape, compound leaves, opposite arrangement, etc.) and then clicks on the SEARCH button.  This results in a list of plants, often with images, that have these characteristics. One then examines the list and looks for a plant that is most similar to the unknown plant. This approach is being used by several applications (apps) developed for mobile devices (e.g., smartphones).   Such as: Smithsonian's  leaf Snap for the iPhone and PlantNet (Plant Identification) for Android phones.
  • A database search is also used in the woody plant identification system of the Oregon State Univ. Landscape Plants website.   See Woody Plant Search.