Rarity refers to the pattern of distribution and abundance of a species, while endangerment refers to factors that make a species vulnerable to decline and extinction. In other words, just because a plant is rare does not necessarily mean it is endangered. However, rare species are generally more vulnerable to endangerment and extinction than common ones are.
Some common species are in jeopardy due to exotic pests or diseases.
Although the roots survive and resprout, the tops are killed by the disease before they can mature, and so the trees cannot reproduce. All commonly occuring species are rare somewhere, usually at the peripheries of their geographic ranges. Although scientists are concerned about the increasing extirpation of local populations of many plants and its effect on these species' gene pools, it is important to distinguish between the plants that are rare locally and those that are rare globally, because the latter are in greater immediate danger of extinction.