An autumn- and spring-germinating annual found in bare patches of thin, dry soil overlying hard igneous rock in open areas within wind-cut heath near the sea. In Ireland it sometimes grows in areas where burning has taken place the previous year. It may occur with a sparse growth of other small annuals, and is typically found in lichen-rich communities. Lowland.
Although T. guttata varies greatly in numbers from year to year, its overall distribution is stable. Most populations are small but show very high levels of genetic variation and diversity.
Light (Ellenberg): 9
Moisture (Ellenberg): 2
Reaction (Ellenberg): 5
Nitrogen (Ellenberg): 1
Salt Tolerance (Ellenberg): 0
January Mean Temperature (Celsius): 5.7
July Mean Temperature (Celsius): 15.5
Annual Precipitation (mm): 1069
Count of 10km squares in Great Britain: 5
Count of 10km squares in Ireland: 10
Count of 10km squares in the Channel Isles: 4
RDB Species Accounts
Tuberaria guttata (L.) Fourr. (Cistaceae)
Spotted rockrose, Cor-rosyn Rhuddfannog
Status in Britain: VULNERABLE.
Status in Europe: Not threatened. Near Endemic.
The habitat of T. guttata is invariably thin soil overlying hard igneous rock near the sea. It grows most abundantly at sites with plenty of bare ground, and its immediate and most dominant associates are generally Cladonia and Polytrichum species (typically C. portentosa and P. juniperinum), together with frequent Aira praecox, Scilla verna and Sedum anglicum. These pockets of skeletal soil are usually found within a more closed community of Calluna vulgaris, Carex panicea, Erica cinerea, Festuca ovina and Ulex gallii, in which T. guttata can, however, also occur. These associates reflect the low nutrient status and the mixture of drought and brief waterlogging to which the habitat is prone.
This species is an annual, flowering and seeding in May and June. Mature plants may be only 6 cm tall, and the flowers, which can be quite conspicuous, may last for only a few hours, dropping their petals by midday. In a warm rainy summer, T. guttata can complete its life cycle within a matter of weeks, but the more typical pattern is late summer germination, followed by an overwintering rosette. This species shows an adaptive plasticity in its morphology, to the extent that the dwarf maritime ecotype in Wales (and in Ireland) was formerly treated as an endemic taxon, ssp. breweri (e.g. Clapham, et al. 1962). Recent work suggests, however, that these populations, at the edge of their range and long-isolated, have developed a unique pattern of genetic variation, and one which is now equally disjunct and broken within Wales (Kay & John 1995). Subspecific status for British plants is not considered appropriate, though recognition at a lower taxonomic level may be so (Stace 1991).
T. guttata is confined to North Wales. Most populations are on the west coast of Holy Island, Anglesey, between South Stack and Rhoscolyn. Away from this area, the only other known colonies are on the north-west coast of Anglesey and on the Lleyn peninsula. Tens, if not hundreds of thousands of plants have been recorded at each of its six major sites. In some years, however, plants may appear only in their hundreds, and in widely scattered tiny patches. Three populations (one of which has not been refound in recent years) have never exceeded 500 plants, and at some sites in some years the plant has not appeared at all. The Lleyn population is tiny, with only about 30 plants in 1993. When not flowering, this small species is inconspicuous, and some small populations might still be overlooked on Anglesey and Lleyn.
It is not yet clear if a recent series of local absence and low numbers reflect temporary seasonal downturns, perhaps as a consequence of poor weather conditions, or is part of a long-term decline. At all but one site, however, there are worrying signs that poor annual performance is due to adverse management, such as heather burning, scrub overgrowth, fertiliser drift, and nutrient enrichment from overwintering livestock - all part of the ongoing isolation of rocky heath outcrops within a landscape of grazing 'improvement', housing development, and caravan parks.
T. guttata occurs in western and south-western Ireland, and in the Channel Islands (Jersey and Alderney). Elsewhere in Europe it is found in the Mediterranean region, extending northwards in western Europe to north-west Germany. It is also occurs in the Canary Islands.
For further reading on the ecology and taxonomy of this species, see Proctor (1960; 1962) and Gallego & Aparicio (1993).
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.
Atlas text references
Atlas (60b) Curtis TGF, McGough HN.
1988. The Irish Red Data Book. 1. Vascular Plants. Kay QON, John R.
1995. The conservation of scarce and declining plant species in lowland Wales: population genetics, demographic ecology and recommendations for future conservation in 32 species of lowland grassland and related habitats. (Science Report No. 110). Meusel H, Jäger E, Rauschert S, Weinert E.
1978. Vergleichende Chorologie der zentraleuropäischen Flora. Volume 2. 2 vols. Proctor MCF.
1960. Biological Flora of the British Isles. No. 72. Tuberaria guttata (L.) Fourreau. Journal of Ecology. 48:243-253. Wigginton MJ.
1999. British Red Data Books. 1. Vascular plants, edn 3.