It may be stating the obvious but the nature of the soil in any one place will have a profound effect on the flora which grows there. The underlying rock affects the extent to which soil is either acidic or alkaline. Calcareous rocks such as chalk and limestone are alkaline and Dorset has a lot of limestone along its coast line as well as chalk on the Purbeck ridge and the north Dorset ridge. The early gentian (Gentianella anglica) is a very uncommon little flower that thrives on limestone.
The early gentian is similar to the more familiar autumn gentian but somewhat smaller and flowers in May and early June where as the autumn gentian flowers in Late August and in September. Early gentian is restricted mainly to limestone and can be found at Durlston and Portland whereas autumn gentian likes chalk and so is more widespread in the county.