These are all plants from the same original form or Genus. The genus name in this example is "Pinus".
A species is a group of plants that have all originated from the same form (Genus), that all resemble each other, that all propagate by spreading their own seeds, and that all have the first part of their specie name in common. By convention, specie names consist of 2 parts, the first part always starting with a capital letter and the second part always starting with a lower case letter. In addition, specie names are also written in italics. For example:
|Pinus sylvestris -- "Scotch Pine"|
|Pinus strobus -- "White Pine"|
|Pinus rigida -- "Pitch Pine"|
Plants within the same genus each vary slightly depending on soil conditions, climate, cultivation method, etc. Examples of slight variations include, flowers differing in color, fruit differing in flavor, leaves differing in form, etc. So, Lemon Verbena (Aloysia citrodora) grown in one country may taste slightly different from Lemon Verbena (Aloysia triphylla) grown in another country. The point is, both Lemon Verbena plants are from the same genus (Aloysia) but since they differ slightly due to climate conditions, etc. they each have their own distinct specie name.
For the purposes of aromatherapy, the percentages of oil constituents in a bottle of Lemon Verbena from Aloysia citrodora might only vary slightly from the percentages of oil constituents in a bottle of Lemon Verbena from Aloysia triphylla assuming the same distillation process was used for both.
Or, the oil constituents could quite possibly vary by a sizable amount. Some examples of oils that vary by a large amount depending on the specific species involved would be Rosemary, Thyme, and Eucalyptus, just to name a few.
With this in mind, finding a bottle of "essential oil" in a store that only says "Chamomile" on it without any specific plant specie name should leave a question in your mind. Do they mean German Chamomile (Matricaria recutita), Moroccan Chamomile (Chamaemelum mixtum), or Roman Chamomile (Anthemis nobilis), or Wild Chamomile (Ormenis multicaulis)? Or perhaps something else?