Racomitrium lanuginosum

Racomitrium lanuginosum is a widespread species of moss found in montane and arctic tundra across the Northern and Southern hemispheres. It grows as large mats on exposed rock and in boulder scree, particularly on acidic rocks. Its leaves have a characteristically decurrent and toothed hair-point, which gives rise to its regional common names woolly fringemoss, hoary rock-moss and woolly moss. Racomitrium lanuginosum grows as 'large cushiony mats'. Its stems are up to 12 centimetres (4.7 in) long and irregularly branched. The leaves are 3–5 millimetres (0.12–0.20 in) long, 0.6–0.9 mm (0.02–0.04 in) wide, lanceolate, pointed and with a strong midrib. They end in a long, thin hair-point, with teeth along both sides pointing 40°–90° from the axis of the leaf. The hyaline (transparent) margins of the hair-point are decurrent along the sides of the leaf. Especially when dry, these hair-points give the plant a downy appearance, which is referenced in several of the common names for the species. Sporophytes are rarely produced, although they are reported to be abundant in coastal areas. The capsules are 1.0–1.7 mm (0.04–0.07 in) long, smooth and brown, and contain spores, which are 8–12 μm long. The form of the hair-points on the leaves of R. lanuginosum is unique among mosses. Racomitrium lanuginosum is 'one of the few bryophytes familiar to many non-bryologists'. Other species that may be confused with it include R. canescens and its close relatives, R. heterostichum and Hedwigia stellata. Racomitrium lanuginosum grows from sea level to the alpine zone, particularly among boulder scree and on exposed rock surfaces. It will also grow in tundra or bogs. It is more frequently found on acidic rocks than calcareous ones. Racomitrium lanuginosum has a circumpolar distribution in the Northern Hemisphere, and is found disjunctly in the mountains of the tropics and the Southern Hemisphere. Within North America, R. lanuginosum is found widely across northern Canada, and extends further south both in the east (to Maine), and in the west (to California and the Rocky Mountains). It is also found in Costa Rica and in mountainous regions of South America and South Africa. In the Atlantic Ocean, isolated population occur on Azores, the Canary Islands, Madeira, Tristan da Cunha and South Georgia; it also occurs on Réunion in the Indian Ocean, in New Zealand, Hawaii and the sub-Antarctic islands Deception Island, Kerguelen, Îles Crozet, Heard Island and the Prince Edward Islands.