Geobotany is the science of the distribution of plants according to geographical and ecological factors. Part of geobotany is phytosociology.
For an understanding of geobotany it is crucial to know plant species as we geobotanists conclude from them to the ecological conditions.
An example: Why is there so much rosemary on Ibiza? One reason of course is that it's a plant of the Mediterranean climate. Another answer is that it likes lime soils. And a very important answer: With the deforestation by humans the garrigue came to be, where plants like rosemary and different species of thyme and lavender are typical, which prefer open sites. Rosemary also grows in the forest but in less quantity.