Pillwort

Pilularia globulifera

Description/identification

Pillwort is a very distinctive little grass-like plant. It is in fact an aquatic fern with thin, thread like leaves which unfurl from tight coils as it grows. It has hard spore cases ‘the pills’ at the base of the stems. In the right conditions it forms a creeping mat over bare mud at the margins of ponds and lakes which make it look like a miniature bright green lawn.

Habitat

Pillwort is a specialist of bare pond edge habitats. It is not a good competitor and only thrives where there are few other plants. Its key habitat requirements are:

• Seasonally fluctuating water levels – it favours temporary pond margins.
• Poaching and grazing by livestock which create bare open margins.
• Slightly acidic ponds on clays, sands and peaty substrates. Pillwort persists at pH 6.
• Open habitats including heathland and acid grassland. It is intolerant of shading from scrub.

Occasionally found in larger ponds and lakes, particularly sand and gravel pits, but only where there is fluctuating water levels and suitable management

Distribution and threats

Unfortunately Pillwort is declining rapidly throughout its north-west European range and the UK now holds a substantial proportion of the global population. Historically it occurred in about 250 ten km squares in the UK, but is now restricted to just a handful of scattered locations (map from species dossier). It still has some strongholds, including the New Forest.

It is principally threatened by 1) habitat loss; through land use change, intensification of farming practices, infilling of ponds, 2) loss of grazing, 3) nutrient enrichment.