Cirsium palustre (L.) Scop., Marsh Thistle

Account Summary

Growth form and preferred habitats

A tall, hairy, wintergreen, monocarpic biennial or perennial, with a single unbranched stem arising from a short, erect, rootstock, attached to a taproot and fibrous roots (Sell & Murrell 2006). The immature plant consists of a large, flat rosette up to 70 cm across of very spiny, ± deeply pinnately lobed, purple-tinged leaves which are hairy above, somewhat cottony with cobweb-like hairs on the underside and have prominent woody veins. The erect, flowering stem, up to 150 cm tall, can be either tall and slender or shorter and more stout, yellowish-green or tinged brownish-purple in colour, furrowed and narrowly winged, the wings being armed with numerous, long, slender spines. The stem leaves are soft and hairy, shallowly to deeply pinnatifid, their short stalks continuing as very spiny, decurrent wings running down the stem. The stem is scarcely branched, except in the uppermost portion, which in late summer has each shoot terminating in clusters of 2-4 almost sessile, dark crimson-purple, flower-heads or capitula (Melderis & Bangerter 1955; Butcher 1961; Grime et al. 1988, 2007).

Marsh Thistle, as its English common name indicates, prefers damp or wet growing conditions and can also tolerate semi-shaded conditions. Together these properties enable it to grow in a wide range of habitats, including woodland clearings and margins, open scrub, marshy stream- ditch- and river-banks, lakeshores with variable water-levels, hollows in rough grassy roadsides, waste ground and moist, poorly drained pastures in both disturbed and undisturbed sites. It can also occur on cliffs, damp walls and in quarries, especially in limestone areas.

C. palustre can grow on a wide variety of soils, most typically mildly acidic, moderately fertile ones, but is absent from strongly acid soils below about pH 4.5 (Salisbury 1964; Grime et al. 1988, 2007). It is particularly associated with damp, acidic lowland habitats, but it reaches its highest B & I elevation at 845 m on Great Dun Fell in Westmorland (VC 69) (F.H. Perring, in: Preston et al. 2002).

Marsh Thistle is especially frequent in limestone areas of Fermanagh and, in the lowlands, it is very common, sometimes locally abundant, in marshes and fens where the surface soil is damp in summer and has a tendency to flood in winter. On upland slopes, it is frequent in damp, rough grassland and by flushes.

The established strategy of C. palustre is categorised as intermediate between Competitive Ruderal and a more general C-S-R, ie a combination of all three basic strategies, Competitor, Stress-tolerator and Ruderal (Grime et al. 1988, 2007).

Variation

Plants in B & I are believed to be much more spiny than those in continental Europe, so that Sell & Murrell (2006) have suggested they might be recognised as a distinct subspecies. In the meantime, Sell & Murrell (2006) recognise two ecotypes within the species, which they name var. palustre and var. ferox Druce. The former is the tall variety with, "Stem up to 150 cm, with long ascending-arching branches and clusters of capitula at the end of each branch.". In comparison, they describe var. ferox as, "Stem up to 50 cm, even more spiny than var. palustre, with capitula in a tight cluster at the end of the stem and not branched.". These varieties have not been identified yet in any Irish Flora.

Flowering reproduction

C. palustre reproduces entirely by wind-dispersed seed, flowering taking place between July and September. Flowering usually occurs in the second year of growth but, if disturbed, or conditions are less than ideal (eg shade, temporary drought, grazing pressure), young plants can remain in a vegetative state for two-three years before attaining the ability to flower. Flower-heads usually occur as clusters of three or more in the axils of the upper leaves, plus more of them crowded at the top of the stem, sometimes making the plant look quite top-heavy (Hutchinson 1972). The clustered thistle flower-heads are small, ovoid, measuring only 12-20 mm across, although the number of florets can be as many as 50 in each one. The capitula are also often present in very large numbers per plant. The usual flower colour is purple, but white heads are not uncommon and pink heads may occasionally be found (Green 2022). The involucral bracts (phyllaries) are narrow, appressed in five-seven rows and are tipped with small, prickly points.

The flowers are usually all bisexual but occasionally some heads are male only. The corolla of each floret is narrow, tubular and 5-lobed and they are pollinated by many kinds of insect visitors, including bees, butterflies, moths and flies, their nectar being more accessible than in other Cirsium species (Sell & Murrell 2006). However, a moderate degree of selfing can also take place, which tends to produce smaller numbers of larger seed than would normally occur. The selfed seeds also show reduced dormancy when compared with crossed ones (van Leeuwen 1981). Fruiting occurs from August to October, the ellipsoid, hairless, dark brown achenes (single-seeded dry fruits), 3.0 × 1.5 mm, with rather polished surface and faintly vertically striate, are produced in very large numbers.

Seed production figures are high, Salisbury (1964) estimating around 70,000 for a particularly large individual which had no less than 1200 flower-heads. He estimated that more normal-sized specimens would produce at least 7,000 seeds. The achene (or seed) is surmounted by a pappus of dirty, white, feathery branched hairs which acts as a parachute for wind dispersal (Salisbury 1964). The current author (RSF) has not located any measurements of seed dispersal efficiency, but it would probably be similar to that of C. vulgare (see that species account for details). In N America, where C. palustre is a serious invasive weed, during stormy weather seeds have been reckoned, "to travel upwards of several kilometres" (Soons 2006).

Marsh Thistle usually occurs as scattered individuals and, unlike numerous other thistles, it seldom occurs in clumps, largely on account of the absence of either a spreading underground rhizome or aerial stolons. Having said this, in suitable, sufficiently damp, moderately disturbed or neglected, ecologically open, waste ground, it can become well established and locally abundant.

The seeds germinate in the spring though the species is capable of forming a persistent seed bank (Grime et al. 1988, 2007). The survey of soil seed banks in NW Europe contains 34 estimates of C. palustre seed survival with records appearing in all four seed bank types: 16 as transient (less than one year); seven as short-term persistent (one-five years); four as long-term persistent (longer than five years) and seven records as being present in the soil, but not able to be assigned to one of the three previous categories (Thompson et al. 1997). As with other thistles, the seedlings require fairly short grassland or open vegetation with bare patches to allow establishment of the young, low-growing leaf rosette.

The plant, even when young, is well protected from grazing by its spines, so in Fermanagh it is particularly frequent in grazed damp meadows around our lake shores.

Hybrids

C. palustre forms natural hybrids with several other members of the genus Cirsium, but only one of these, that with C. dissectum (C. × forsteri), a distinctive intermediate that K.J. Walker (in Stace et al. 2015) has described as, "the most frequently recorded Cirsium hybrid in B & I", has been recorded in Co Fermanagh (see the current author's account on this website).

C. palustre also hybridises quite frequently with C. heterophyllum in N Britain, very rarely with C. acaule and quite frequently with C. arvense in Britain, although the latter hybrid has only been found once in Ireland, making it very likely that it is under-recorded here (K.J. Walker, in: Stace et al. 2015).

Fossil record

As with other thistles, fossils of C. palustre have been recorded time after time in a succession of interglacial periods in B & I, including the Late Weichselian and the late Flandrian (the Littletonian in Ireland). In the current Flandrian interglacial, sites include those of Neolithic, Bronze Age and Roman dates, some of the sites occurring at high altitude where woodland cover was less dense. As Godwin (1975) comments, "The record certainly offers a basis for regarding C. palustre as a persistent native species, at least from Weichselian time.".

Fermanagh occurrence

Marsh Thistle is the most abundant and widespread member of the genus Cirsium in Fermanagh by quite a margin. It has been recorded in 494 tetrads, 93.6% of the VC total, while its nearest competitor, C. arvense (Creeping Thistle), scores only a 80.9% tetrad presence. As the VC presence statistics indicate, it is widespread throughout the county, absent only from the most acidic soils and from the deepest shade.

British and Irish occurrence

C. palustre is an extremely successful species, being common and widespread throughout B & I. The hectad map indicates it is absent only from the area around the English Wash and from the northern tip of the Scottish Outer Hebrides (VC 110) (Perring & Walters 1962, 1976; Preston et al. 2002).

European and world occurrence

C. palustre is common across temperate regions of Europe and adjacent Asia, although it is rare in the Mediterranean basin. There are also rare outliers in N Africa and further east into C Asia. In Scandinavia, the species commonly occurs to almost 65^oN, and it is present at lower frequency well inside the Arctic Circle (Godwin 1975). Marsh Thistle is introduced in several widely disjunct areas of the globe, including N America, the Kerguelen islands (also known as the Desolation Islands) in the Southern Indian ocean and in New Zealand, where mention of it was first published in 1772 (Hultén & Fries 1986, Map 1865; Webb et al. 1988).

Uses

Like other thistles, the stem of Marsh Thistle is edible if properly prepared and cooked. Grieve (1931) reports that it was previously regarded as being, "as good as the Milk thistle, which surpasses the finest cabbage".

Weed control

Effective weed control is achieved by cutting after the flower-heads begin to develop but before the achenes begin to mature. Cutting too early, before the plant's food reserves have passed from the stem to the developing inflorescences, merely allows the plant to survive, recover and convert into a triennial or short-lived perennial. Repeated mowing or cutting at the root of the plant with a spade in spring are effective mechanical means of reduction, if not giving total control. Re-sprouting is a common response to mechanical methods of thistle cutting and removal, so repeated treatment over several years is necessary. For larger infestations, chemical methods of control are required. Fortunately the species is susceptible to herbicides such as glyphosate, MCPA and 2,4-D (Salisbury 1964).

Names

The genus name 'Cirsium' is said to be derived from the Greek 'kirsos', a swollen vein, alluding to the reaction when the skin is pricked by the spines (Hyam & Pankhurst 1995). The Latin specific epithet 'palustre' refers to the typical habitat occupied and means 'of swampy places' from 'palus' and ūdis', 'swamp' or 'bog' (Gilbert-Carter 1964).

The English common name 'Marsh Thistle' is equally clear regarding the typical growing conditions occupied by the plant. A previous botanical name for the plant was Carduus palustris L., and under this moniker it supported several additional English common names including 'Bog-thrissel', 'Moss-thristle', 'Water Thistle' and 'Red Thistle' (Britten & Holland 1886).

Threats

None.

References

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