(where marram grass may be locally abundant) and stony mountain tops and plateaux. The total number of species is large; 84 have been recorded on the verges of a single road in West Lothian. Smooth Meadow-grass and Broad-leaved Meadow-grass are widespread in damp lowland conditions, Wood Sedge (Carex sylvatica) in woodlands, and Oval Sedge and Early Hair-grass on upland moors. In damp conditions Phragmites reeds and several species of Juncus are found abundantly including Jointed Rush, Soft Rush and Toad Rush, and less commonly the introduced species Slender Rush. Common Cottongrass is a familiar site on marshy land, but Saltmarsh Sedge (Carex salina) was only discovered for the first time in 2004 at the head of Loch Duich. Endemic species Shetland Mouse-ear (Cerastium nigrescens) is an endemic plant found in Shetland. It was first recorded in 1837 by Shetland botanist Thomas Edmondston. Although reported from two other sites in the 19th century, it currently grows only on two serpentine hills on the island of Unst. The Scottish Primrose (Primula scotica), is endemic to the north coast including Caithness and Orkney. It is closely related to the Arctic species Primula stricta and Primula scandinavica. Young's Helleborine (Epipactis youngiana) is a rare endemic orchid principally found on bings created by the coal-mining industry in the Central Lowlands and classified as endangered. The St Kilda Dandelion (Taraxacum pankhurstianum) is a species of dandelion endemic to the island of Hirta, identified in 2012. Rare species Some of Scotland's flowering plant species have extremely restricted ranges in the country. These include Diapensia lapponica, found only on the slopes of Sgurr an Utha, Argyll and Mountain Bearberry, recorded at only a few mainland locations, and on Skye and Orkney. The pinewoods of Strathspey contain rare species such as Creeping Lady's Tresses, Twinflower and the One-flowered Wintergreen. Plans to protect the Intermediate Wintergreen, also found here, were introduced in 2008. Other nationally rare species include Tufted Saxifrage, Alpine Catchfly, Sword-leaved Helleborine, Norwegian Sandwort, Dark-red Helleborine, Iceland Purslane, Small Cow-wheat and Yellow Oxytropis. Invasive plants A number of non-native, invasive species have been identified as a threat to native biodiversity; Giant Hogweed, Japanese knotweed, Himalayan balsam and Rhododendron ponticum are generally regarded as the 'big 4'. In May 2008 it was announced that psyllid lice from Japan, which feed on the Knotweed, may be introduced to the UK to bring the plant under control. This would be the