Discovery of new Australasian Rare Earth Element hyperaccumulator ferns from screening herbarium specimens

Background and Aims: Rare Earth Elements (REE) are essential for the development of clean technologies. Forecast demand for REE will not be met by current supply, increasing the risk of REE supply-chains, and understanding the effects of their extraction on the environment remains limited; therefore, new approaches and techniques are required. Hyperaccumulators (plants with a tendency to accumulate specific elements in their tissues) can be used to remove metals from contaminated soils. This study aimed to discover new REE hyperaccumulators in the Australasian region among the Blechnaceae and Gleicheniaceae families using specimens stored at the Queensland Herbarium. Methods: A handheld X-ray fluorescence (XRF) instrument was harnessed to scan herbarium specimens, and this data was analysed with Dynamic Analysis in GeoPIXE software. Seven specimens with high yttrium were considered for further analyses to validate the XRF results: elemental analysis was conducted with inductively coupled plasma optical emission spectroscopy (ICP-OES), an elemental distribution mapping through micro-X-ray fluorescence (µXRF) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS) to rule out airborne contamination of plant samples. Results: From the 3256 specimens analysed with the handheld XRF analysis, 73 specimens met the criteria to be considered REE hyperaccumulators (yttrium > 50 µg g⁻¹ in the XRF analysis). Among this group, 11 new hyperaccumulator taxa were discovered, and the elemental analysis for selected species reported a total REE concentration around 1000 µg g⁻¹, i.e. Diploblechnum neglectum (978 µg g⁻¹), Sticherus flabellatus var. flabellatus (1130 µg g⁻¹), and Sticheropsis milnei (1290 µg g⁻¹). Furthermore, we validated the high REE hyperaccumulating capacity of the previously reported fern species Blechnopsis orientalis (3850 µg g⁻¹ total REEs) and Dicranopteris linearis (1280 µg g⁻¹ total REEs). Conclusions: The use of non-destructive handheld XRF analysis to screen herbaria collections is an efficient tool to discover new hyperaccumulator plants and this information could also be used as a bioprospecting tool to find REE deposits for mining and/or for future REE phytomining.