The rarest of rarities in the flora of Mexico

Abstract

Background: Endemism can originate from multiple biogeographic and evolutionary processes that promote the formation or persistence of species with restricted distributions (rare species). Understanding rare species’ distributions is a central question in biogeography and is crucial for biodiversity conservation. Questions: What are the rarest plant species in Mexico? How are they distributed? Under what risk categories should they be classified? Studied species: Vascular species considered rare in the flora of Mexico. Study site: Mexico. Methods: “Rare species” were defined as species endemic to Mexico whose distribution is restricted to a single 1 × 1° cell. We analyzed rare species’ distributions and proposed the risk category for each according to IUCN criteria. For some of the species distributed in the cell with the highest number of rare species, we compared the proposed category with published evaluations. Results: We identified 2,705 rare species. The richest cells in terms of rare species are in southern Mexico. Only 302 species had been previously evaluated under IUCN criteria. The remaining 2,403 qualify for the Near Threatened (NT) category or higher. The cell with the highest rare species richness, located in the Sierra Norte of Oaxaca, contained only 10 species with an existing IUCN risk category; for another 81 species, the categories of Vulnerable (VU), Endangered (EN) or Critically Endangered (CR) are indicated. Conclusions: Recognizing the rarity of these 2,705 species will increase attention on them, allowing more precise appraisal of their extinction risk and possible strategies for their conservation.