This diminutive, loosely tufted, spring-germinating annual occurs in seasonally wet, compacted open ground such as in gateways and on wheel tracks, less often in natural areas of erosion and in quarries, on serpentine heathland. Lowland.
Populations of J. pygmaeus vary greatly in size from year to year, but there has been a strong decline since 1950, mainly due to tracks becoming abandoned and vegetated over, or infilled with hardcore.
Light (Ellenberg): 9
Moisture (Ellenberg): 7
Reaction (Ellenberg): 4
Nitrogen (Ellenberg): 2
Salt Tolerance (Ellenberg): 0
January Mean Temperature (Celsius): 6.7
July Mean Temperature (Celsius): 15.9
Annual Precipitation (mm): 965
Count of 10km squares in Great Britain: 4
Count of 10km squares in Ireland: 0
Count of 10km squares in the Channel Isles: 0
RDB Species Accounts
Juncus pygmaeus L.C.M.Rich. (Juncaceae)
Juncus mutabilis Lam.
Status in Britain: ENDANGERED.
Status in Europe: Not threatened.
J. pygmaeus is a diminutive annual, restricted to the serpentine, gabbro and Crousa gravel heathlands of the Lizard peninsula. It is among the most threatened of the Lizard's special plants. Typically J. pygmaeus is a plant of seasonally-flooded rutted tracks and gateways, where the drier Erica cinerea-Agrostis curtisii 'short heath' grades into wetter Erica vagans-Schoenus nigricans 'tall heath'. On tracks it grows on shallow loess largely bare of other vegetation or in an open community of other small wetland species, including Juncus bulbosus. It is also more rarely recorded from the shallow margins of natural erosion pans, from cob and borrow pits, and in wet ground in serpentine quarries. In all instances, disturbance, typically rutting by vehicles on trackways (and, traditionally, poaching by cattle in gateways), is essential to the survival of this small annual. Such ephemeral habitats are of exceptional botanical importance, and rarer associates of J. pygmaeus include Cicendia filiformis, Juncus capitatus (infrequently), Pilularia globulifera, Radiola linoides, Ranunculus tripartitus, and nationally rare cryptogams such as Cephaloziella dentata and Chara fragifera.
The plant germinates in spring as water levels decline and temperature rises, maturing on the exposed mud in early summer. The rate and timing of the drop in water level are critical in determining the size and vigour of populations. In good years some of the larger Lizard colonies number thousands of individuals, whilst in poor years, for instance 1994, the plant may perform very badly, the total British population numbering only a few hundred plants.
Since 1950, J. pygmaeus has been recorded from about seventeen 1 km squares. However, since 1980 it has been reported from thirteen, and since 1990 from only five, only two of which lie within SSSIs. Some colonies are very small and sporadic in appearance. A main factor in its decline is the cessation of the traditional use of the ancient trackway systems, which rapidly leads to a growth of coarse perennials, including Agrostis canina, Glyceria declinata, Juncus bulbosus and Scirpus fluitans, and ultimately overgrowth by scrub species (e.g. Salix cinerea). However, seed may remain viable in the soil for very many years, and it is possible that J. pygmaeus might reappear if disused tracks are opened up. The infilling of track systems using hardcore (as witnessed recently on one protected site) is likely to lead to a permanent loss. There is an urgent need for the restoration of habitats suitable for this species.
Outside Britain, J. pygmaeus occurs locally in western and southern Europe northwards to Denmark, and in north-west Africa and Turkey.
A. J. Byfield
PLANTATT - Attributes of British and Irish plants. (.zip 1455KB) This dataset was compiled and published in 2004, and last updated in November 2008. Download includes an Excel spreadsheet of the attributes, and a PDF explaining the background and nomenclature. Note that the PDF version is the booklet as published, whereas the Excel spreadsheet incorporates subsequent corrections. A hardcopy can be purchased from the Centre for Ecology and Hydrology.