A large proportion of the UKs chalk grassland is found in Wiltshire, where the vast military estate of Salisbury Plain is the single largest remaining tract of unimproved calcareous grassland in northern Europe. Other special chalk downland sites include Pewsey Downs and Coombe Bissett Down. Morgan's Hill near Calne is home to the UK's only downland site for Marsh Helleborine Epipactis palustris. The Upper Thames catchment, in the north of the county, has some of the country's best remaining hay meadows. North Meadow near Cricklade and Clattinger Farm support populations of Fritillary Fritillaria meleagris, Downy-fruited Sedge Carex filiformis
and Green-winged Orchid Anacamptis morio as well as numerous other species indicative of unimproved neutral grassland. Wiltshire is a predominantly arable county and is of international importance for its populations of scarce arable 'weeds'. Among these are Venus's Looking Glass Legousia hybrida, Dense-flowered Fumitory Fumaria densiflora
and Narrow-fruited Cornsalad Valerianella dentata. The county is also home to many ancient woodlands including Savernake Forest, near Marlborough, with its veteran trees and a strong population of Violet Helleborine Epipactis purpurata. Other notable woodlands include Clouts Wood, near Swindon, home to Bath Asparagus Ornithogalum pyrenaicum
and Collingbourne Wood, near Tidworth, which supports Meadow Saffron Colchicum autumnalis,
Wood Vetch Vicia sylvatica and Herb-Paris Paris quadrifolia.