A perennial herb of old chalk and limestone grassland, often on slopes with a N. or N.W. aspect, and sometimes occurring in rank swards. It spreads by producing axillary basal rosettes to form clonal patches, and also reproduces by seed. Lowland.
This species is declining in its two main areas in Wiltshire and Glamorgan. The reasons for the decline include habitat destruction by ploughing, coastal erosion, changes in land management and, particularly in Wiltshire, hybridisation with Cirsium acaule. It became extinct as a native in its sole Cambridgeshire locality in 1973, but has subsequently been re-introduced there.
Suboceanic Southern-temperate element.
Light (Ellenberg): 8
Moisture (Ellenberg): 6
Reaction (Ellenberg): 8
Nitrogen (Ellenberg): 3
Salt Tolerance (Ellenberg): 0
January Mean Temperature (Celsius): 3.9
July Mean Temperature (Celsius): 16.1
Annual Precipitation (mm): 882
Count of 10km squares in Great Britain: 17
Count of 10km squares in Ireland: 0
Count of 10km squares in the Channel Isles: 0
Atlas Change Index: 0.41
RDB Species Accounts
Cirsium tuberosum (L.) All. (Asteraceae)
Tuberous thistle, Ysgallen Oddfynog
Status in Britain: VULNERABLE.
Status in Europe: Not threatened. Endemic.
In Britain, the largest surviving populations of C. tuberosum grow in species-rich ancient chalk and limestone grassland, often on slopes with a northerly or north-westerly aspect. Typical associates include Carex flacca, Centaurea scabiosa, Dactylis glomerata, Festuca rubra, Helictotrichon pubescens, Sanguisorba minor, Serratula tinctoria and Succisa pratensis, with Bromopsis erecta, Filipendula vulgaris and Genista tinctoria in its Wiltshire sites.
It is a long-lived herbaceous perennial which spreads slowly by the production of axillary basal rosettes to form densely-leafy clonal patches, sometimes a metre or more in diameter. When vigorous and ungrazed, it may dominate or even exclude other vegetation. Flowering begins in late June and peaks in July, with a few heads continuing to appear through August and into September. In Welsh populations the erect flowering stems are typically 50-60 cm high with a single capitulum, but in Wiltshire they grow to 100 cm and bear two or three capitula. Flowers are produced freely by some plants, but rather sparsely or not at all by others, even when vegetative growth is vigorous. The flowers are visited by bumble-bees (Bombus species) and butterflies. Pollen fertility is high in apparently 'pure' populations in Wales and Wiltshire, and isolated plants are self-compatible, although seed-fertility is variable and sometimes low.
C. tuberosum has a disjunct distribution in Britain, now growing only in a group of about 8-10 limestone grassland sites along 5 km of the coast of south Glamorgan, and in a series of increasingly scattered downland or old pasture localities in Wiltshire (Grose 1957), where there are at least seven extant colonies (Everett 1993), and Dorset, where one small population is known (Mahon & Pearman 1993). It also grew on an ancient grassy trackway in Cambridgeshire, but became extinct there in 1974, although plants from the original stock were reintroduced to a nearby site in 1987, with initial success (Pigott 1988).
Threats come from habitat destruction by ploughing, coastal erosion, changes in land management, and especially from hybridisation with Cirsium acaule and perhaps other Cirsium species. A local threat from rabbits, and perhaps other small mammals, which dig for the edible tubers of C. tuberosum, was successfully countered in a small Glamorgan population by wire netting laid on the soil surface (Kay & John 1995). In Wiltshire, many populations appear to have been severely affected or swamped by hybridisation with C. acaule. Here, a few refuges for C. tuberosum are found on unploughed north-facing slopes with tall swards unsuitable for the low-growing, thermophilous C. acaule. Genetic surveys indicate that the Glamorgan populations of C. tuberosum are little, if at all, affected by hybridisation with C. acaule, which is at the limit of its British range there.
C. tuberosum has a wide but scattered distribution in western and west-central Europe, normally growing in rather damp calcareous grassland. It is closely related to Cirsium dissectum and the European species C. filipendulum and C. rivulare, which show varying degrees of ecological, morphological and geographical distinction.
Q. O. N. Kay
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
1994. Population genetics and demographic ecology of some scarce and declining vascular plants of Welsh lowland grassland and related habitats. Science Report No. 93.
1992. Vergleichende Chorologie der zentraleuropäischen Flora. Volume 3. 2 vols.
1999. British Red Data Books. 1. Vascular plants, edn 3.