Cirsium dissectum (L.) Hill, Meadow Thistle

Account Summary

Growth form and preferred habitats

Cirsium dissectum is a rosette-forming 'hemicryptophyte' (Greek = 'half hidden'), having its dormant buds at soil surface level, a short, ascending perennial rootstock and the bulk of its foliage basal. The plant develops short, spreading stolons that can grow to around 40 cm long, enabling formation of dense clonal patches by vegetative reproduction in all the habitat types it occupies. In this way C. dissectum spreads and, since it is long-lived, it can become locally abundant, even in areas of B & I where it is otherwise scarce (de Vere 2007; S. Smith & C. Rimes, in: Stroh et al. 2019).

C. dissectum produces erect, usually solitary flowering stems, 15-80 cm tall, lightly covered with white hairs. The basal rosette leaves are elliptic-lanceolate, up to 25 × 3 cm, long-stalked, bristle-tipped, lightly covered with white cottony hairs above and more densely felted with them beneath. The leaves are wavy, toothed or sometimes slightly pinnately lobed, their margins armed with soft prickles that provide very little protection from grazing animals (de Vere 2007). The flowering stem is also covered with cottony white hairs and usually bears a few small, bract-like leaves in its upper half, that are oblong-lanceolate, their bases half-clasping the stem and producing small basal auricles.

Flower heads are usually solitary, rarely two or three on a common stalk, 2.5 cm diameter, involucral bracts (phyllaries) purplish, appressed, connected with long, woolly hairs. The outer involucral bracts are spine-tipped, inner acuminate and the bisexual flowers are mauve-purple (Hutchinson 1972; Sell & Murrell 2006; de Vere 2007).

Bog or Meadow Thistle is an excellent indicator of lowland, species-rich, base-rich, nutrient-poor, constantly damp to wet, often peaty or gleyed soil habitats. C. dissectum is very typical of long-established, poorly drained, tall herb 'water meadows' or 'fen-meadows' (ie of the vegetation type NVC M24 Cirsio-Molinietum caeruleae Sissingh & De Vries (Rodwell et al. 1991b)).

Elsewhere in Britain and Ireland, in the last 40 years, these water meadows or pastures have become severely depleted due to extensive, expensive, EC-funded drainage operations. The same grants and processes encouraging farmers to aim for increased agricultural production have applied in Fermanagh, but while some drainage has taken place, the enormous extent of these summer grazing wet meadows within the Fermanagh boundary has allowed many of them to survive unaffected. The more recently switched funding emphasis in areas of marginal farming activity towards conservation and set-aside will probably prevent any more drainage in this area of Fermanagh.

C. dissectum is essentially a species of wet to damp ground, including nutrient-poor grasslands, fens, bogs, heaths and sand-dune slacks, but it can survive limited periods of summer drought, although the stress and wilting involved does affect subsequent growth and reproductive success (de Vere 2007). Observation indicates that the species prefers well-lit places, but it can survive in conditions of partial shade. In Britain, Hill et al. (1999) gave it a light indicator value of 8, "representing a light-loving plant rarely found where relative illumination in summer is less than 40%" (de Vere 2007).

The established strategy of C. dissectum is categorised by Grime et al. 1988, 2007) as being SC/CSR, meaning it is intermediate between a Stress-tolerant competitor and a more general balance of all three strategies, Competitor, Stress-tolerator and Ruderal.

Fossil record

There is no specific fossil record of Cirsium dissectum in B & I, despite the pollen and achene both being quite distinctive in appearance (Godwin 1975; de Vere 2007). However, the current author (RSF) is not a palynologist and the pollen and fruits of the species clearly must not be sufficiently distinctive to be reliably distinguished from those of other species in the genus.

Flowering reproduction

Flowering takes place between late May and July, ripe seed heads appearing throughout July and August. The number of florets in a capitulum can vary from 20 to 160 and the flowers produce both a sweet perfume and plentiful nectar, attracting a range of insect visitors that include butterflies, bees and long-tongued flies as pollinators (de Vere 2007). Although the perfect (ie bisexual) flowers are obviously evolved for, and are, mainly, cross-pollinated, the flowers are also self-compatible, any selfed flowers, as usual, producing fewer seeds than out-crossed ones. Experimental measurements showed capitula selfed with a paintbrush suffered an almost 90% reduction in seed production compared to those out-crossed using the same pollination method (de Vere 2007).

The mean number of seeds per flowerhead in Britain has been shown to be very variable, ranging from just 6.5 in a population in Wales, to 82.7 in one in Devon (de Vere 2007). A five year study monitoring C. dissectum populations in three grasslands in the Netherlands found the levels of flowering, in terms of numbers of florets per head and seeds per flower, varied significantly during the study period (Jongejans et al. 2006).

Seed dispersal

Achenes of C. dissectum are pale brown, obovoid and either smooth (Sell & Murrell 2006) or vertically ribbed and striate (Butcher 1961), 2.2-4.0 mm in length, with a distinct apical collar and a long (10-20 mm) pappus of pure white, plumose bristles that often becomes detached before the seed is shed from the fruiting capitulum (de Vere 2007). When the feathery pappus is attached, it allows wind dispersal to operate during dry weather, but in wet conditions the hairs congeal, rendering the dispersal mechanism ineffective. The plant, being monocarpic, dies after fruiting and the capitulum eventually breaks off and drops any seed it contains near the parent plant position (de Vere 2007). Even with the benefit of an attached pappus, experimental studies of the distances travelled by C. dissectum seeds, using average wind speeds during the dispersal season at the chosen localities, found that few moved more than 10 m from the parent plant. The simulated experimental measurements suggest the dispersal potential of C. dissectum is lower than that of C. vulgare (Spear Thistle) and C. eriophorum (Woolly Thistle) (Klinkhamer et al. 1988; Tofts 1999).

Seed germination and seedling establishment

Experimental studies found C. dissectum seed could germinate over a wide range of temperatures and other simulated field conditions, but seedling establishment in experiments where seed was added to field vegetation was low; natural establishment is very rarely observed. This being the case, it is clear from the population dynamics that the dominant method of reproduction in C. dissectum is by vegetative propagation and populations are clonal (de Vere 2007).

Fruiting capitula collected from 22 populations across B & I found rather high levels of seed predation, eg up to 63% of capitula showing some evidence of predation at Lough Bunny in the Burren, Co Clare (H9) (de Vere 2007).

There are no statistics available or estimates given for the longevity of seed survival in the soil seed bank (Thompson et al. 1997; de Vere 2007).

Hybrids

C. dissectum can form intermediate hybrids with C. palustre (Marsh Thistle) quite frequently in both B & I since both species are wetland ones, and with C. acaule (Dwarf Thistle) extremely rarely (Stace et al. 2015). See the account of the C. palustre hybrid (C. × forsteri) on this website.

Fermanagh occurrence

Meadow Thistle has been recorded in 180 Fermanagh tetrads, 34.1% of those in the VC. It is most frequent in the Western Plateau on wet peat, or on soils that are subject to water-logging in winter along rivers and streams or on lakeshores. It is also very frequent around Upper Lough Erne and other lakes, in bogs, 'fen-meadows' and marshy ground that is base-poor and moderately acid. Locally, C. dissectum can also occur in damp peaty soils formed directly over limestone, as for example at Marble Arch, Legacurragh and Knockmore.

In Fermanagh, C. dissectum is frequently found with Succisa pratensis (Devil's-bit Scabious) and an attractive array of orchids sometimes accompany it, including several Dactylorhiza spp. (Marsh-orchids), Gymnadenia conopsea (Chalk Fragrant-orchid), Listera ovata (Common Twayblade), Orchis mascula (Early-purple Orchid), both Platanthera spp. (Butterfly-orchids) and Pseudorchis albida (Small-white Orchid).

British and Irish occurrence

C. dissectum has a rather unusual extreme Atlantic distribution in the British Isles and in Europe, and belongs to the Oceanic West European phytogeographical element. Unfortunately, the species appears to be in decline in at least certain areas of its overall range (Perring & Walters 1962, 1976; Fitter 1978; F.H. Perring, in: Preston et al. 2002).

In Britain, it was previously widespread in the lowlands S & E of a line from NE Yorkshire to Pembrokeshire (Perring & Walters 1962, 1976). However, in recent years, it has declined significantly in England, and the BSBI Monitoring Scheme estimated a decline of -28% (Rich & Woodruff 1990). Against this trend, C. dissectum was first recorded in Kintyre (VC 101) in 1976 and in a damp field in W Cornwall (VC 1) in 1983. Stace (1997) mentions that C. dissectum now occurs 'very locally' in SW Scotland (VCs 101, 102).

A 30-year study of vegetation communities in three valley mires or bogs in Suffolk showed that C. dissectum disappeared from all but one of the sample areas due to lack of traditional management (ie dereliction), changes in water regime (essentially drainage, coyly referred to as 'dewatering') or increasing fertility from runoff of agricultural fertilisers, slurry and increased levels of atmospheric nitrogen from traffic emissions. The Suffolk community where C. dissectum presence actually increased was a M13 Schoeno-Juncetum short sedge mire, which deteriorated due to drainage into a dry variant of M24 Molinia caerulea-Cirsium dissectum fen meadow (Fojt & Harding 1995).

In Ireland, Meadow or Bog Thistle is relatively common, but it is much more frequent in the western half of the island, especially N of the Shannon estuary. The isolated, disjunct occurrence of C. dissectum in SW Scotland (Kintyre (VC 101) and S. Ebudes (VC 102)) remains a biogeographical puzzle, but it might well prove an introduction from adjacent NI.

European and world occurrence

The distribution of C. dissectum mapped for the British Isles and N Europe by Fitter (1978), shows the species on continental Europe mainly represented in France, the occurrence becoming fragmentary northwards in Belgium, Netherlands and N Germany. It thus appears more or less restricted to the milder, wetter, most oceanic parts of the continent, in parallel with its preferences in B & I (S. Smith & C. Rimes, in: Stroh et al. 2019). Spain is an additional territory mentioned in Flora Europaea 4, which also indicates that the species occurs or has occurred as an introduction in Hungary and Norway, and possibly in N Italy although the latter requires confirmation (Tutin et al. 1976; Pignatti 1997).

C. dissectum is now an endangered species in NW Germany having suffered a great decline attributed to the decimation of fens and bogs, intensification of drainage schemes and the increased use of fertilisers (Buck-Sorlin 1993). A similar sudden decline has occurred during the last few decades in the Netherlands, which has been attributed to increasing soil acidification, possibly operating through aluminium toxicity (de Graaf et al. 1997).

Names

In the past, Cirsium dissectum was known as Carduus pratensis, which led to it being given the English common names 'Meadow Thistle' and 'Marsh Plume Thistle' (Hutchinson 1972). Two other English names given by Britten & Holland (1886) are 'Gentle Thistle', the plant being relatively unarmed with spines, and 'Pig-leaves', as the plant, being ± unarmed, is readily grazed by stock animals. Britten & Holland (1886) remark that, "the name 'Gentle Thistle' was invented by Dr. J. Hill (Herb. Brit., 1769), and applied by him to Carduus pratensis L., and Saussurea alpina L., from their thistle-like inflorescence and smooth foliage.".

Threats

Agricultural improvements, including drainage and extensive use of fertilisers, together with acidification and atmospheric nitrogen pollution from traffic emissions, plus natural succession in the wet and moist habitats it occupies have all been negative pressures on populations of C. dissectum.

References

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