lochs and 6,600 river systems. Below the tree line there are several zones of climax forest. Birch dominates to the west and north, Scots Pine with Birch and oak in the eastern Highlands and oak (both Quercus robur and Q. petrea) with Birch in the Central Lowlands and Borders. Much of the Scottish coastline consists of machair, a fertile dune pasture land formed as sea levels subsided after the last ice age. Machairs have received considerable ecological and conservational attention, chiefly because of their unique ecosystems. Flowering plants and shrubs 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). Nonetheless, there are a variety of important species and assemblages. Heather moor containing Ling, Bell Heather, Cross-leaved Heath, Bog Myrtle and fescues is generally abundant and contains various smaller flowering species such as Cloudberry and Alpine Ladies-mantle. Cliffs and mountains host a diversity of arctic and alpine plants including Alpine Pearlwort, Mossy Cyphal, Mountain Avens and Fir Clubmoss. 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 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 common 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