The total number of vascular species is low by world standards, partly due to the effects of
Pleistocene glaciations (which eliminated all or nearly all species) and the subsequent creation of the
North Sea (which created a barrier to re-colonisation). On the
Hebridean islands of the west coast, there are
Plantago pastures, which grow well in locations exposed to
sea spray and include
red fescue,
sea plantain and
sea pink. The machair landscapes include
rare species such as
Irish lady's tresses,
yellow rattle and numerous
orchids along with more common species such as
marram grass and
meadow buttercup,
ragwort,
bird's-foot trefoil and
ribwort plantain. Scots lovage (
Ligusticum scoticum) first recorded in 1684 by
Robert Sibbald, and the
oyster plant are uncommon plants of the coasts.
Aquatic species Bogbean and
water lobelia are common plants of moorland pools and lochans. The
least (
Nuphar pumila),
yellow and
white water-lilies are also widespread.
Pipewort has generated some botanical controversy regarding its discovery, classification and distribution. It was found growing on
Skye in the 18th century, although there was subsequent confusion as to both the discoverer and the correct scientific name – now agreed to be
Eriocaulon aquaticum. The European range of this plant is confined to Scotland and western Ireland and it is one of only a small number of species which is common in North America, but very restricted in Europe. There are a few localised examples of the
rigid hornwort (
Ceratophyllum demersum).
Grasses and sedges Grasses and sedges are common everywhere except
dune systems (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
rough 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. Endemic species of the
Hieracium,
Rubus and
Taraxacum apomictic complexes occur in Scotland, such as the
St Kilda dandelion (
Taraxacum pankhurstianum), endemic to the island of
Hirta, identified in 2012, the orange-flowered hawkweed (
Hieracium fulvocaesium), endemic to Strathnaver, the Shetland Hawkweed (
Hieracium zetlandicum), endemic to the Shetland Islands, and
Rubus longiflorus, endemic to coastal Angus and Kincardine.
Rare species '') Some of Scotland's flowering plants 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. Young's helleborine (
Epipactis helleborine var. youngiana) is a rare endemic
orchid principally found on
bings created by the
coal-mining industry in the
Central Lowlands and classified as endangered.
Invasive plants Some 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 first time that an alien species has been used in Britain in this way. Scientists at the Commonwealth Agricultural Bureaux International did not believe the lice would cause any environmental damage. Over-grazing caused by the large numbers of
red deer and sheep has also resulted in the impoverishment of moorland and upland habitats and a loss of native woodland. In 2012, the Scottish Government published a "Code of Practice on Non-Native Species" to help people understand their responsibilities and provide guidance as to which public body has responsibility for the various habitats involved. ==Naturalised plants==