1 Kwantlen Polytechnic University. Plant Database. School of Horticulture, 2015. Web. 21 Sept. 2015. <https://plantdatabase.kwantlen.ca/plant/search.gsp>.
This is a fantastic resource. It has wonderful pictures detailing all parts of the tree/shrub (incl. fruit, flowers, leaves, form, etc). In addition, the layout is simple, easy to follow, and it is the most comprehensive of the three sources. Do note, it is heavy on plant vernacular. It does not list the cultivars, nor does it offer a thorough detailing of the plants limitations. Furthermore, I found the search bar to be slightly finicky and at times the only way I could pull up a plant was to manually search for it in the index. But these are minor issues compared to the benefit it has to offer. The only major drawback was that it did not contain all of the plants on the list!
2 Dirr, Michael. Manual of Woody Landscape Plants. Champaign, Illinois: Stipes Publishing Company. 1983. Print.
This resource nicely lists common cultivars, and landscape value. However, many of the plants on List 1 were however not found in this book. There are no photos, only hand-drawn sketches; which is beneficial to help show you leaf structure, but you miss out on colours and overall form. It is also very comprehensive but for this level of course, it goes into excess detail. It is also uses very subjective language. However, I would still recommend this book as a resource since it was comprehensive enough that I did not need to visit another source when it contained a tree/shrub I was looking for.
3 University of Connecticut. Plant Database. College of Agriculture, Health and Natural Resources, 2014. Web. 21 Sept. 2015. < http://www.hort.uconn.edu/plants/index.php>.
Good resource to find some of the more obscure trees and shrubs. However, on its own, it is not comprehensive enough to answer all of the ID questions. It provides several nice photos however not all parts of the trees/shrubs are photographed (ie. Some trees did not have photos of their flowers, etc). It does however provide a good list of landscape uses and liabilities. This resource is much less heavy on the vernacular and therefore is more user-friendly towards those just starting out. In summary, this is a good secondary resource. However, there are many other resources like this one out there and it definitely does not stand out from the rest.