Illinois Threatened and Endangered Plant S-Rank Update and a New Illinois Plant Watch List

In order to determine how to prioritize protection for plant species, it is necessary to assess their conservation status. State threatened and endangered (T&E) species lists are useful for determining conservation priorities, but listing criteria differ by state, so aligning priorities across political boundaries can be difficult. NatureServe is a conservation nonprofit that assesses conservation status ranks for species and ecosystems in the United States and Canada at the global level (G-ranks) and national level (N-ranks), and oversees member programs that assess ranks at the sub-national level (S-ranks). Ranks are generally assessed from a scale of 1 (Critically Imperiled) to 5 (Secure) using a calculator that weights rarity, threats, and trends categories. Illinois had not updated plant S-ranks since 1987, when ranks were based on less explicit criteria and there was no rank calculator. We assessed S-ranks for Illinois plants in 2023 and compared them to previous ranks assessed in 1987. We compared 2023 S-ranks to our state T&E listing status in order to determine if they were correlated. In addition, we created an Illinois Plant Watch List for species that did not qualify for state listing but were vulnerable and needed conservation attention. In 2023, species were ranked as less imperiled overall than in 1987, likely because of better population information as a result of more field surveys and attention. We also found that S-ranks were related to listing status in Illinois, which is not surprising given that they rely on similar components to determine if a species is at risk. Updated S-ranks will likely be relied upon to inform species listing decisions, determine survey priorities, and help inform land protection efforts.