Mr. Smarty Plants is very happy that you find our Native Plant Database useful in your planning. I think you are asking about the difference between Size Notes and Size Class found under PLANT CHARACTERISTICS on the species page for the different plants in our Native Plant Database. Size Class is a way to categorize the plants into size groups. One way this data can be used is to search for plants of a particular size in our Native Plant Database using the COMBINATION SEARCH option. For instance, if you were looking for shrubs in Texas no taller than 5 feet, you would enter "Texas" under Select State or Province, "Shrub" under Habit (general appearance) and "3-6 ft." under Size Characteristics to get a list of more than 70 shrubs within that size category. You can also search by size class if you use any of the lists on our RECOMMENDED SPECIES page by using the NARROW YOUR SEARCH in the side bar when you open any of the lists. Size Notes, on the other hand, gives you information about the size of the particular species for that page. For instance, on the page for Juniperus ashei (Ashe juniper) you see that it is in the 12-36 ft. Size Class and its Size Notes say "Rarely grows over 30 feet tall." You will probably notice that most plants have data for the Size Class, but some do not have data for Size Notes since those are more specific. As we learn the specifics of the size of individual species they are added to the Native Plant Database.