The descriptive text, below the map, is from the Cornish Red Data Book (2009). The map on this web page depicts the organisms distribution and shows the records made pre-2000 and those made since.
This is a species found in calcareous water over peaty or sandy substrata and may behave as an annual or perennial. Currently it is known from 30 or more sites in Britain which, outside of East Anglia, are widely scattered with records from Cornwall, South Wales, Anglesey, Scotland (as far north as Shetland) and Northern Ireland. Most of the extant sites are near the coast. It is relatively widespread in Ireland. In Cornwall it is only recorded from the Lizard Peninsula: Countybridge Quarries, Mullion Cliffs and Predannack Downs, together with an older record from Hayle Kimbro Pool. At all of these sites it grows in water overlying ultramafic serpentine rock, which have sandy-gravel or peaty substrates. The most significant threat to this species, like many stoneworts, is nutrient enrichment. Shade cast from the invasion of scrub is also a threat. Algal blooms, which may be suggestive of nutrient enrichment, have been reported in at least one site on the Lizard, may cause problems by smothering the colony of stonewort. In Britain the Lesser-bearded Stonewort is classified as Nationally Scarce (Near Threatened). It is a UK Biodiversity Action Plan (BAP) species with its own Species Action Plan (SAP). It also receives general protection under the Wildlife & Countryside Act 1981. Most of the Lizard sites are on SSSIs and National Nature Reserves.
I.J. Bennallick, S. Board, C.N. French, P.A. Gainey, C. Neil, R. Parslow, A. Spalding and P.E. Tompsett. eds. 2009. Red Data Book for Cornwall and the Isles of Scilly. 2nd Edition.Croceago Press.
The Cornish Red Data Book Project was led by the Cornwall and Isles of Scilly Federation for Biological Recorders (CISFBR). The full text and species accounts (minus the maps) are available on the CISFBR website.