yx yxw zy 2009 Soil and Biota of Serpentine: A World View Northeastern Naturalist 16(Special Issue 5):111–120 Adiantum viridimontanum, Aspidotis densa, Minuartia marcescens, and Symphyotrichum rhiannon: Additional Serpentine Endemics from Eastern North America Tanner Harris 1 and Nishanta Rajakaruna 2,3,* Abstract - Serpentine outcrops around the world are known to harbor disproportion- ately high rates of plant endemism. Remarkable cases of serpentine endemism occur in New Caledonia and Cuba, with 3178 and 920 endemic taxa, respectively, found solely on serpentine. Despite the patchy occurrence of serpentine in eastern North America from Québec and Newfoundland south to Alabama, only one taxon, Cerastium veluti- num var. villosissimum, has been broadly recognized as a serpentine endemic for the region. Based on reports in the literature, we suggest that Adiantum viridimontanum, Minuartia marcescens, and Symphyotrichum rhiannon be considered endemic to serpentine soils from the east coast of North America. Aspidotis densa, with several disjunct populations on and off serpentine in western North America, is known solely from serpentine soils where it occurs in eastern North America and should be consid- ered endemic to the substrate there. The geobotany of eastern North America in general is poorly understood, and additional taxonomic studies on the region’s unique geologic substrates will likely yield further edaphic endemics. Introduction Narrow endemism can result from any number of biological and en- vironmental interactions. However, within a regional climate, geological discontinuities, both topographic and geochemical, are the most common and striking influences of narrow endemism (Kruckeberg 1986, Kruck- eberg and Rabinowitz 1985). Among the endemic species resulting from geological discontinuities are edaphic endemics, those species restricted to chemically and/or physically unique soils (Rajakaruna and Boyd 2008). Edaphic endemics are often either products of recent in situ evolution re- sulting from divergence following colonization of a new substrate (i.e., neoendemics; Baldwin 2005, Ramsey et al. 2008) or are relicts that have ex- perienced a reduction in their geographic or ecological ranges as a result of altered climatic or biotic conditions (i.e., paleoendemics; Kruckeberg 1986, Raven and Axelrod 1978). Recent investigations of edaphically restricted taxa provide compelling evidence in support of both modes of origin for edaphically endemic taxa (Gottlieb 2004, Mayer and Soltis 1994, Mayer et al. 1994, Pepper and Norwood 2001). 1 Department of Plant, Soil, and Insect Sciences, University of Massachusetts, Fer- nald Hall, 270 Stockbridge Road, Amherst, MA 01003. 2 College of the Atlantic, 105 Eden Street, Bar Harbor, ME 04609. 3 Current address: Department of Biological Sci- ences, San José State University, One Washington Square, San José, CA 95192-0100. * Corresponding author - Nishanta.Rajakaruna@sjsu.edu.