Vascular plants can be rare for an astonishing variety of reasons.
Natural rarities, therefore, are those species that always have been rare during their evolutionary history, or currently are rare by today's standards. Each general class of rarity has its own set of consequences that must be considered for a rare species' conservation and management. Rarity, in fact, describes at least three different biological possibilities. Consideration of such patterns of distribution and abundance, coupled with other inherent biological characteristics, allows rare species to be grouped into distinct classes. Classifications are essential to articulating what differences actually distinguish classes, in this case, of plant rarity, ultimately leading to protection efforts that can be tied explicitly to individual classes of rare species.