This subspecies of the perennial knawel is a small, inconspicuous and prostrate plant. It has brittle, woody stems and the five sepals have prominent white borders. The small flowers appear between June to September.
In spite of the name perennial knawel usually behaves as a biennial plant, living for two years. The Breckland subspecies is thought to flower all year round on occasions but usually flowers during the summer months.
This subspecies is found only in the Breckland region of East Anglia although it has been recorded on six other sites outside Breckland, all in Norfolk. The nominate race, Scleranthus perennis perennis is widespread throughout central and southern Europe and the range extends into north-west Europe where it is in decline. Britain represents its furthest north-western outpost where it is known from only one single site in mid-Wales.
Prefers the open, sandy, acidic soils characteristic of the Brecks. Breckland is an area where average annual rainfall is low and the soils are free-draining and of poor quality. The prostratus subspecies of perennial knawel is associated with uncompacted tracks and close-cropped grassland. Being a poor competitor it requires open soil for germination.
Neither of the two subspecies of perennial knawel have been historically plentiful in Britain. The Breckland subspecies has only been recorded from 25 sites, and never more than six at any one time. The survival of the plant has also been threatened by loss of habitat. During the 20th century, much of the Breck has been lost to afforestation, agricultural improvement and development. In addition, traditional grazing by sheep and rabbits has fluctuated through declining stock values and the effects of myxomatosis on rabbit numbers. Many of the perennial knawel's former sites have become unfavourable for it through an increase in more dominant vegetation and encroachment of gorse and Scots pine seedlings.
Scleranthus perennis ssp. prostratus has been included in English Nature's Species Recovery Programme. In 1996, Yvonne Leonard, a botanist living in the East Anglian Brecks, produced a Species Action Plan for this subspecies. The objectives were to reinstate viable populations of the plant on at least three of its former sites. This involved a study of the plant to ascertain its requirements and to assess the suitability of former site for a re-introduction programme. In partnership with local landowners, the two local county trusts, local authorities and the Royal Botanic Gardens, Kew, plants were germinated and a 'nursery' set up to supply plants for re-introduction. Some 11 plots were chosen and regular monitoring has taken place to establish whether conditions and management were suiting the plants. There has been some success with these re-introductions but it is still too early to say that the perennial knawel has been preserved as a naturally occurring species. With much of the trial area within a large, privately owned farm, maintaining the ideal conditions for the plant relies heavily of the co-operation of the landowner and the management by farm contractors.
The UK Biodiversity Action Plan for this species is available at UK BAP.
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