Lichens of ultramafic substrates in North America: a review

Abstract

Lichens are among the most prominent and successful life forms of metal-rich habitats, including ultramafic rocks and soils; however, research on lichens of ultramafic habitats is limited, especially on the North American continent. This review examines geographic and ecological patterns of ultramafic lichen assemblages by synthesizing published reports of lichens of ultramafic substrates in North America, and by creating a database characterizing the ecology and habitat (substrate type, pH affinity, geographic distribution) for all taxa recorded in the literature. This effort yielded a total of 437 lichen species and infraspecific taxa reported from ultramafic substrates in the published literature. Lichen assemblages of ultramafic substrates vary in composition and are dominated by acidophytic taxa with a minor, but consistent, basiphytic component. Species lists from ultramafic habitats in different geographic regions varied widely, suggesting that factors unrelated to substrate, such as climate, have a large effect on lichen assemblage composition. However, several studies showed clear differentiation between lichen composition on nearby or adjacent ultramafic and nonultramafic habitats, suggesting that ultramafic substrates harbor regionally unique lichen assemblages.