Collema nigrescens
Collema nigrescens has become rarer and is disappearing from severely disturbed areas in Italy (Zedda, 2002), while in Canada it has a Nova Scotia Probincial Status of Yellow. Species designated with a Yellow status may need particular attention to avoid becoming extinct (Cameron & Neily, 2008).
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Lichenized, cyanobiont is Nostoc
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The foliose thallus of Collema nigrescens reaches 2-10 cm in diameter and is epruinose and glossy. It is dark olive-green or olive-brown, partly yellowish green in between ridges, and yellow-tinted olive-green on the lower surface. The broad lobes measure 0.5-1.0 cm across and have continuous margins and rounded apices. Pustules and ridges are prominent on the lobes. Isidia are not usually present, but are globular and up to 0.2 mm in diameter when they occur. Apothecia are very frequent, with epruinose discs measuring 0.4-1mm wide. The ascospores are needle shaped to bacilliform, (4)5- 12-septate, and 50-90 x 3-4.5 μm in size (Brodo et al, 2001; Park, 1990; Zedda, 2002; Purvis et al, 1992).
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Collema nigrescens has approximately an East temperate and Pacific Northwest distribution in North America (Brodo et al, 2001). It is distributed throughout regions of Europe with a suboceanic climate(Zedda, 2002). This species occurs in the United States, South Korea (Park, 1990), Sweden, Greece, Siberia, Canada (Degelius, 1974), North Africa (Purvis et al, 1992), Philippine Islands (Herre, 1951), and Bermuda (Riddle, 1916).
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Collema nigrescens is corticolous, growing on both deciduous and coniferous trees (Park, 1990) such as Acer rubrum (Cameron & Neily, 2008), Sorbus, Fraxinus, and Populus(Santesson et al, 1984) among others. It also grows on decayed wood (Harris, 1904), epiphytic mosses and sometimes on rock. It often grows in humid, lighted conditions and in preserved forests (Zedda, 2002).
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