Herbarium and field studies of nickel hyperaccumulator plants from ultramafic soils in Guatemala

Until 2019, there were no published reports of trace element hyperaccumulation in the plants of Central America or Mexico. Recent reports, based mostly on measurement of herbarium specimens using x-ray fluorescence (XRF) spectroscopy, have begun to identify hyperaccumulators of nickel (Ni) in this region. The most extensive deposits of Ni-rich ultramafic rocks and soils in Central America occur along the Polochic-Motagua fault system in eastern Guatemala. This study focused on discovery and characterization of new hyperaccumulators in Guatemala, starting with surveys of herbarium specimens, followed by field studies to understand the ultramafic soils of the region and the ecology of hyperaccumulators that occur there. Initial XRF screening at the Missouri Botanical Garden Herbarium, along with two herbaria in Guatemala, identified four previously unreported Ni hyperaccumulators—Arachnothryx linguiformis, Arachnothryx buddleioides, Chionanthus panamensis, and Orthion guatemalense. Field studies in Guatemala characterized the communities in which these species occur, some of which include multiple hyperaccumulator species growing in close proximity. In two taxa that showed phenotypic variation in foliar Ni concentration, there was no statistically significant correlation between Ni concentrations in leaves and either the total or DTPA-extractable Ni in soils, suggesting that other genetic or environmental variables may influence hyperaccumulation.