The specific epithet caerulea means "deep blue" and refers to the purple spikelets.Molinia caerulea (purple moor-grass) is a species of flowering plant in the grass family Poaceae, native to Europe, west Asia, and north Africa. It grows in locations from the lowlands up to 2,300 m (7,546 ft) in the Alps. Like most grasses, it grows best in acid soils, ideally pH values of between 3.5 and 5, however, it can continue to live under more extreme conditions, sometimes to as low as 2. It is common on moist heathland, bogs and moorland throughout Britain. Introduced populations exist in northeastern and northwestern North America.
Molinia caerulea is an herbaceous perennial bunchgrass (tussock-forming), growing up to 90 cm (35 in) tall (taller when sheltered by gorse and heather), with many closely packed stems. The leaves are coarse, green, taper to a point, long, flat and sometimes slightly hairy on top. Due to the dense tussock it is very resistant to heath fires. Its ligule is a ring of hairs, as in heath grass (Danthonia decumbens). The long narrow purple spikelets are a major identification feature - the panicle is 15 cm (6 in) long.
It flowers between July and September, later than any other species.
The caterpillars of some Lepidoptera use it as a foodplant, e.g., the chequered skipper (Carterocephalus palaemon).
Claviceps purpurea is an ascomycetous fungus which grows on the seeds of purple moor grass.
Purple moor grass and rush pastures is a United Kingdom Biodiversity Action Plan, on account of its rarity.
M. caerulea is cultivated for its panicles of purple spikelets on yellow stems. In cultivation it grows to 1.5 m (5 ft) tall by 40 cm (16 in) broad. Numerous cultivars have been selected, of which M. caerulea subsp. caerulea 'Variegata' has gained the Royal Horticultural Society's Award of Garden Merit.