Changes in taxonomy, threats, and distribution affect the extinction risk of rare U.S. orchids

Background/Question/Methods

Successful conservation efforts rely upon integrated, up-to-date, and readily available information on the biology and conservation status of a species. We completed 28 assessments of rare U.S. orchids using the most current methodology for NatureServe Conservation Status Ranks and the IUCN Red List. Nine of the taxa are listed as Threatened or Endangered under the Endangered Species Act, seven are endemic to a single state, and all but two were assessed as globally Critically Imperiled (G1) or Imperiled (G2) before review. Assessments were based on a thorough review of each taxon’s ecology, distribution, threats, population (size and trends), biology (including pollinators and mycorrhizal associates), taxonomy, and conservation efforts. We used occurrence data to develop range maps and calculate Area of Occupancy and Extent of Occurrence. We updated NatureServe’s Global Ranks for all taxa, completed new draft Red List Assessments for 27 taxa, and updated the Red List Assessment for Platanthera praeclara.

Results/Conclusions

Draft Red List assessments indicate that 14 taxa are threatened with extinction (Critically Endangered, Endangered, or Vulnerable) and 11 taxa are not threatened (Near Threatened or Least Concern). Similarly, we found that 50% of orchids assessed are Imperiled (G2), while nearly a third are Critically Imperiled (G1), according to NatureServe’s Global Conservation Status Ranks. Habitat loss or conversion, from development to agriculture, threatened almost every orchid assessed. Significant data gaps still impede conservation status assessments and subsequent actions. Despite the known importance of mycorrhizal fungi for orchid germination and growth, we documented fungal associates for only 9 of 28 taxa assessed. The rank for Triphora amazonica is now GU (“unrankable”), due to a taxonomic change resulting in insufficient information, and 3 taxa are Data Deficient under Red List Criteria. Revisions in NatureServe’s Ranks demonstrate changes in conservation status over time. Rank revisions in this study include increased extinction risk for 2 taxa and decreased extinction risk for 7 taxa. New interpretation of information for Malaxis wendtii and Triphora yucatanensis, including population declines in the latter, led to increased extinction risk. Recently discovered populations of the federally listed Isotria medeoloides resulted in decreased extinction risk for this taxon. Extinction risk decreased for 6 taxa due to taxonomic revisions, new data, or updated methodology. This study demonstrates that current surveys and basic research are still needed to record rare plant abundance and threats, and to track trends over time.