Molinia caerulea

Description

Molinia caerulea is a perennial herbaceous bunchgrass (tussock-forming), growing up to 120 cm 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 long.

It flowers between July and September, later than any other species.

Ecology

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 were a United Kingdom Biodiversity Action Plan habitat, on account of their rarity.

However, in 2025 it was reported that purple moor grass was spreading over Britain and displacing other vegetation in a way characteristic of invasive species, although it is native. Over the previous fifty years it had spread over large upland areas in much of Wales, Dartmoor, Exmoor, the Pennines, the Peak District, North York Moors, Yorkshire Dales and many parts of Scotland. Areas of moor grass support very little bird or insect life – a characteristic described as a "terrestrial dead zone" or desert – and is difficult for humans to walk through. It is not controlled by herbivores, who will favour other plant species over the grass and will not eat it whatsoever past early summer, when its nutritional value falls heavily. It is also unaffected by disease and the natural successional processes through which grassland typically transitions to other plant communities, such as temperate rainforest.

The cause of the spread is largely human activity: incentives to farmers to raise livestock, and the burning of moorland to produce fresh vegetation for animals, have pushed many environments where Molinia now dominates beyond their capacity to sustain a natural ecological balance. The heavy deposition of nitrogen, which accumulates in rainfall from livestock farming, traffic and industrial sources, and the drainage of naturally-wet peat bogs also contributes. Molinia deep roots protect it from the burning that destroys other, competing, plant species. Most approaches to destroy the invasive Molinia—burning, weedkiller, livestock grazing—only work temporarily, with the moor grass recolonising cleared areas. Approaches such as blocking land drainage to restore its moisture levels, planting sphagnum moss to restore peat bogs, planting trees and excluding livestock are being trialled to combat the issue and restore areas overtaken by Molinia.

Cultivation

Molinia caerulea is cultivated for its panicles of purple spikelets on yellow stems. In cultivation it grows to 1.5 m tall by 40 cm broad. Numerous cultivars have been selected, of which the following have gained the Royal Horticultural Society's Award of Garden Merit:

• M. caerulea subsp. arundinacea 'Windspiel'{{cite web
• M. caerulea subsp. caerulea 'Edith Dudszus'
• M. caerulea subsp. caerulea 'Moorhexe'{{cite web
• M. caerulea subsp. caerulea 'Poul Petersen'
• M. caerulea subsp. caerulea 'Variegata'

Gallery

Image:Illustration_Molinia_caerulea0.jpg Image:Molinia-caerulea.jpg Image:Molinia.jpg Image:Molinia.caerulea.jpg Image:Molinia.caerulea.2.jpg Image:Molinia.caerulea.3.jpg Image:molinia_caerulea.jpeg|Inflorescence Image:molinia_caerulea_habitus.jpeg|Habitus (German Horst) Image:molinia_caerulea_blatt.jpeg|Leaf and vegetative parts Image:Molinia-caerulea-habitat.JPG|Molinia caerulea at natural habitat near Silkeborg, Denmark. File:Claviceps microcephala.jpg|Sclerotium of Claviceps purpurea which grows on the seeds of purple moor grass.

References

References

1. {{BSBI 2007
2. "Molinia caerulea (L.) Moench".
3. Harrison, Lorraine. (2012). "RHS Latin for gardeners". Mitchell Beazley.
4. C. E. Hubbard. (1978). "Grasses: a Guide to their Structure, Identification, Uses and Distribution in the British Isles". [[Penguin Books]].
5. (2009). "Grasses of the British Isles". Botanical Society of the British Isles.
6. (2008). "Purple moor grass and rush pastures". UK Biodiversity Action Plan - Plan Priority Habitat Descriptions.
7. Monbiot, George. (9 June 2025). "There's an invader turning huge swathes of Britain into deserts – and these dead zones are spreading". The Guardian.
8. (2008). "RHS A-Z encyclopedia of garden plants". Dorling Kindersley.
9. (July 2017). "AGM Plants - Ornamental". Royal Horticultural Society.
10. "''M. caerulea'' subsp. ''caerulea'' 'Edith Dudszus'". RHS.
11. "''Molinia caerulea'' subsp. ''caerulea'' 'Poul Petersen'". RHS.
12. "RHS Plant Selector - ''Molinia caerulea'' subsp. ''caerulea'' 'Variegata'".