Pillwort (Pilularia globulifera) is a rather curious member of the fern family. Its leaves resemble green hair, and arise singly from a creeping stem, or rhizome giving it the appearance of a rather untidy green wig. When young, these hair-like leaves are curled at their extreme tips. On the rhizome there is a hard pill-like swelling, giving this plant its common English name.
Pillwort is a true fern and reproduces by spores, which are found in 'sporocarps', hard capsules that may remain viable for many years, but which open when swollen with water to release megaspores, fertilized by the microspores, which are also released.
Pillwort is declining throughout the whole of its western European range. A substantial percentage of the world population is found in Britain. It used to occur in about 250 ten km squares but, since 1970, it has been seen in only 90 of these. The UK population is widely scattered, but there are still some substantial populations and several stronghold areas.
Pillwort is a plant of pond and lake edges, where it is sometimes submerged. It prefers neutral or slightly acid, sedimentary-type soils that have been subject to some disturbance. Its former distribution depended on land-use creating suitable habitats. These include, including millponds and cattle ponds. Recently it has started taking over old sand pits where it grows in shallow water.
The greatest threat to the future of this intriguing plant is the excessive use of herbicides and run-off from nitrate and phosphate fertilisers polluting the water bodies where pillwort grows. Another danger comes from the changing use of ponds and lakes and the loss of the regular disturbance that the plant requires.
There is also the problem of an invasive escape from domestic ponds and garden centres, Australian swamp stonecrop (Crassula helmsii), which in some places has swamped pillwort and many other native pond species wherever it appears.
Pillwort is listed in the UK Biodiversity Action Plans and included in English Nature's Species Recovery Programme. In a survey of threatened British wetland plants commissioned by the plant conservation charity, Plantlife, pillwort communities were examined at four European sites, all in the Sologne region of France. The study revealed that pillwort can survive under at least two different environmental conditions; one on lake edges where the action of waves maintains an open community, and another where regular disturbance results in temporary populations. The report recommended further study into the differing conditions exploited by the plant.
Pillwort, it seems, can be a good early coloniser of suitable habitats, but usually only where there have been historical records of its presence. For proper conservation priorities to be prepared for this species, a full report of its status in Europe is required.
The UK Biodiversity Action Plan for this species is available at UK BAP.
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