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. Hyperaccumulator plants are metal-loving organisms that 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. Selected specimens were further analysed to validate the XRF results: elemental analysis was conducted with inductively coupled plasma optical emission spectroscopy (ICP-OES), an elemental distribution map through micro-X-ray fluorescence (µXRF) and scanning electron microscopy (SEM) to rule out airborne contamination of plant samples. Results From the 3256 specimens analysed with the portable XRF, 73 specimens met the criteria to be considered REE hyperaccumulators (yttrium >50 µg g-1 on XRF analysis). Among this group, 11 new hyperaccumulator taxa were discovered, and the elemental analysis reported a total REE concentration around 1000 µg g-1, i.e. Diploblechnum neglectum (978 µg g-1), Sticherus flabellatus (1130 µg g-1), Sticheropsis milnei (1290 µg g-1). We validated the strong REE hyperaccumulating capacity of the previously reported ferns Blechnopsis orientalis (3850 µg g-1 total REEs) and Dicranopteris linearis (1280 µg g-1 total REEs). Conclusions The use of non-destructive portable XRF to scan herbaria collections is a tool to discover hyperaccumulator plants and this information could also be used as a bioprospecting tool to find REE deposits for potential REE phytomining.