In my lifelong attempts to improve my field naturalist skills, I sometimes run into species that seem so alike that it takes a considerable amount of time to differentiate them in my mind.
Take for example the ash family. (This may be a moot point because of the devastation that that group is suffering due to the Emerald Ash Borer). I very commonly see ash trees, especially young ash trees, during my various walks. But, at first, white ash and red ash (also called green ash) look very much alike. They both have opposite, compound leaves and diamond-shaped ridges in the mature bark. It was only after seeing literally thousands of each species and in all seasons before I started to gain confidence in telling the two apart.
In the world of bird song, there are two spring nesting species of the boreal forest which have songs that are so high in pitch that they approach the limit of human hearing. These are the Cape May Warbler and the Golden-Crowned Kinglet. Each spring, I listen to recordings of each dozens of time in order to remind myself of the subtle differences between the two songs. This way, when I hear a super high pitched song during a breeding bird survey, I am able to tell, with some confidence, which species is singing.
I have a similar difficulty with certain low-growing, ground cover plants (sometimes climbing) such as myrtle, wintercreeper and English Ivy. The three are shiny green all year round and feature at least some white veining on the surface.
Recently, I gathered samples of all three and put them in a vase on my word desk. The following photographs show the clear differences between each species:
Myrtle has egg-shaped, pointed and shiny leaves
Wintercreeper has rounder leaves with teeth and white veining
English ivy has three lobes and white veining