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The serpentine-substrate effect is well documented for vascular plants, but the literature for bryophytes is limited. The majority of literature on bryophytes in extreme geoedaphic habitats focuses on the use of species as bioindicators of industrial pollution. Few attempts have been made to characterize bryophyte floras on serpentine soils derived from peridotite and other ultramafic rocks. This paper compares the bryophyte floras of both a peridotite and a granite outcrop from the Deer Isles, Hancock County, Maine, and examines tissue elemental concentrations for select species from both sites. Fifty-five species were found, 43 on serpentine, 26 on granite. Fourteen species were shared in common. Twelve species are reported for the first time from serpentine soils. Tissue analyses indicated significantly higher Mg, Ni, and Cr concentrations and significantly lower Ca∶Mg ratios for serpentine mosses compared to those from granite. Soil analyses demonstrated significant differences between the two substrates.
Serpentine outcrops are model habitats for geoecological studies. While much attention has been paid to serpentine outcrops worldwide, the literature on eastern North American serpentine and associated biota is scant. This review examines the available literature, published and unpublished, on geoecological studies conducted on serpentine in eastern North America, from Newfoundland through Québec and New England south to Alabama. Most serpentine outcrops in the region have been mapped, but there have been few intensive mineralogical and pedological investigations. The limited soil analyses available suggest elevated levels of heavy metals such as Ni, near-neutral pH values, and Ca∶Mg ratios < 1, characteristic of serpentine soils worldwide. Botanical studies to date have largely focused on floristic surveys and the influence of fire exclusion and grazing on indigenous vegetation. To date, 751 taxa of vascular plants belonging to 92 families have been reported from serpentine outcrops in the region. Two taxa, Agalinis acuta and Schwalbea americana, are federally endangered in the United States while many others are listed as rare, endangered, or imperiled in one or more states or provinces. Globally, six species, Adiantum viridimontanum, Minuartia marcescens, Pycnanthemum torrei, S. americana, Scirpus longii, and Symphyotrichum depauperatum are listed as imperiled (G2) while one species, Agalinis acuta, is listed as critically imperiled (G1). Cerastium velutinum var. villosissimum is the only recognized serpentine endemic plant for eastern North America while Adiantum viridimontanum, Aspidotis densa, M. marcescens, and S. depauperatum are largely restricted to the substrate. Based on current distributions, we propose that A. viridimontanum and M. marcescens be considered endemic to serpentine substrates in eastern North America. Studies on cryptogams list 165 species of lichens and 146 species of bryophytes for the region. None of the species found appear to be restricted to the substrate. Compared to other regions of the world, ecophysiological and evolutionary investigations are scant. Biosystematic investigations are restricted to the taxa Adiantum aleuticum, C. velutinum var. villosissimum, and S. depauperatum. Plant-soil relations, especially the capacity to hyperaccumulate metals such as Ni and the ecological consequences of metal accumulation, are also under explored. One report from eastern Canada lists Arenaria humifusa, M. marcescens, Packera paupercula, and Solidago hispida as hyperaccumulating Ni although the findings have yet to be confirmed by subsequent investigations. Overall, serpentine geoecology in eastern North America remains largely unexplored.
A floristic survey of a polje lakebed, which is full in the spring but drains completely as the season progresses, revealed a community of small mud-bottom plants including the globally rare Coleanthus subtilis, not previously recorded from Northwest Territories, Canada. The newly discovered site is 1077 miles NNW of its nearest North American location in southern British Columbia, which is the northern edge of a region of occurrence including southern British Columbia and the Columbia River in Washington and Oregon. The lakebed flora included four zones of vascular plants. Coleanthus subtilis was confined to the lowest level mud-bottom community, which had been exposed for the shortest period and included a rich assemblage of annuals including Juncus bufonius, Limosella aquatica, and Ranunculus hyperboreus. The lakebed flora included mostly widespread boreal species, and C. subtilis may be included in this category. It appears restricted to specific montane and boreal areas by its requirement of pronounced seasonal inundation in a cool climate. Coleanthus subtilis may have persisted at the Washington and British Columbia locations, near the limit of the continuous montane glaciation, since early postglacial times. The occurrence in Northwest Territories may be either a result of dispersal from unglaciated areas of Beringia nearby to the west or from the south. Although it has sometimes been considered introduced in the United States parts of its North American range, it is here considered native at all of its North American sites on the basis of: (1) its restricted and unusual habitat; (2) global rarity; (3) suffusive rarity, which is known to lead to mistaken assumptions of introduction; (4) occurrence in botanically rich regions and close association with rare native species; (5) relatively early year of collection; (6) distribution corresponding to a well recognized native pattern; (7) lack of evidence of spread to anthropogenic habitats; and (8) the fact that it is easily overlooked by early collectors as a result of only appearing at intervals of several years when water levels have dropped sufficiently.