Declared Rare and Priority Flora List
The Declared Rare and Priority Flora List is the system by which Western Australia's conservation flora are given a priority. Developed by the Government of Western Australia's Department of Environment and Conservation, it was used extensively within the department, including the Western Australian Herbarium. The herbarium's journal, Nuytsia, which has published over a quarter of the state's conservation taxa, requires a conservation status to be included in all publications of new Western Australian taxa that appear to be rare or endangered. The system defines six levels of priority taxa:

X: Threatened (Declared Rare Flora) – Presumed Extinct Taxa
These are taxa that are thought to be extinct, either because they have not been collected for over 50 years despite thorough searching, or because all known wild populations have been destroyed. They have been declared as such in accordance with the Wildlife Conservation Act 1950, and are therefore afforded legislative protection under that act.