Screening for potential metal hyperaccumulator plants in Angola: a herbarium-based approach

Metal hyperaccumulator plants play a key role in understanding plant adaptation to metal-rich soils and offer potential for phytoremediation and phytomining. Angola hosts highly weathered tropical soils, yet its flora remains unexplored, mainly with respect to metal accumulation traits. This study presents the first broad, herbarium-based screening of Angolan plant specimens to identify potential hyperaccumulator taxa and evaluate taxonomic and spatial patterns of metal accumulation. A total of 234 samples from 132 species were analyzed for aluminum, manganese, nickel, copper, iron, cobalt, chromium, cadmium, lead, and zinc using microwave digestion followed by optical emission spectrometry. We identified numerous aluminum hyperaccumulators, particularly within the genus Landolphia, with contents in leaves up to 4.5% of dry mass, and detected extreme manganese accumulation in Landolphia congolensis, exceeding 2% of dry mass. These metal contents markedly exceed previously reported values for most Angolan species and reveal metal accumulation in taxa not previously recognized as hyperaccumulators. We also show strong site dependence of accumulation and consistent differences between plant organs, with leaves generally containing higher metal contents than fruits and inflorescences. Our findings significantly expand the known diversity of African metal hyperaccumulators, demonstrate the high value of herbarium collections for environmental monitoring, and provide a foundation for future work on phytoremediation potential, plant-soil interactions, and implications for human and ecosystem health in Angola.