The IUCN initials stand for the International Union for Conservation of Nature.

The IUCN Red List of Threatened Species attempts to list all those species of Plants, Birds, Reptiles, Amphibians, Fish, Insects and Molluscs that are threatened with extinction throughout the World. The IUCN is based in London, but the list attempts to cover the Whole World. The list is in-complete, especially in regard to plants.

The Current 2006 Red List Categories

• (EX) Extinct : No known individuals remaining.
• (EW) Extinct in the Wild : Known only to survive in captivity, or as a naturalized population outside its historic range.
• (CR) Critically Endangered : Extremely high risk of extinction in the wild.
• (EN) Endangered : High risk of extinction in the wild.
• (VU) Vulnerable : High risk of endangerment in the wild.
• (NT) Near Threatened : Likely to become endangered in the near future.
• (LC) Least Concern : Lowest risk. Does not qualify for a 'more at risk' category. Widespread and abundant taxa are included in this category.
• (DD) Data Deficient : Not enough data to make an assessment of its risk of extinction.
• (NE) Not Evaluated : Has not yet been evaluated against the criteria.

When discussing the IUCN Red List, the official term threatened is a grouping of three categories: Critically Endangered, Endangered, and Vulnerable.

Since the threatened status of plants varies from decade to decade (eg. some that were extant becoming extinct, or extinct plants re-introducing themselves) the Author has not shown the status of the threat to any particular plant.

Further information can be found on Wikipedia :
 IUCN Red List of Threatened Species