Carduus nutans L., Musk Thistle
Account Summary
Introduction, a very rare casual. Eurosiberian temperate, but widely naturalised, including in N America and the southern hemisphere.
1952; MCM & D; waste ground below the old workhouse in Enniskillen Town.
Growth form and preferred habitats
A tall, prickly, biennial or occasionally winter annual thistle, 1.0–1.5 m tall, with large, rounded, solitary, terminal, nodding, reddish-purple flower-heads (capitula), 30-65 mm in diameter, the capitula base covered with reflexed, outer involucral bracts, C. nutans is very distinctive in appearance and easily recognised. The plant develops a long, fleshy taproot and a basal rosette of large, 15-30 cm, elliptic to lanceolate, glabrous to densely pubescent, pinnately-lobed leaves, each lobe ending in a sharp spine. The whitish, cotton-clothed, erect stems are angular, furrowed and partly spiny winged, but are un-winged and leafless for a considerable distance below the capitula (Melderis & Bangerter 1955; Garrard & Streeter 1983; Perring & Walters 1989).
C. nutans grows in rough, often overgrazed, or recently established pasture grasslands, on roadsides and in waste ground, typically on lowland, well-drained, lime-rich soils, or in calcareous, sandy, gravelly or shingly ground near coasts. The less tall, less floriferous, coastal form has been recognised as a separate variety, var. litoralis P.D. Sell (Sell & Murrell 2006). The species reaches its highest altitude in B & I at High Cup Nick in Westmorland (VC 69) at 530 m (F.H. Perring, in: Preston et al. 2002). The established strategy of C. nutans has been categorised as R/CR, meaning it is intermediate between a pure Ruderal and a Competitive Ruderal species (Grime et al. 1988, 2007).
C. nutans was introduced to N America in the mid-19th century, most probably through dumped ships' ballasts and, subsequent to its establishment and dispersal throughout Canada, it arrived in the land-locked province of Saskatchewan. Here it became a serious invasive weed and, in 1970, prior to the commencement of a biological control program, Harris (1984) reported C. nutans densities of up to 150,000 per hectare in pastureland. At one time, C. nutans dominated an area of 30,000 km2 in Saskatchewan (Desrochers et al. 1988). In Canada, it is thought the species may have dispersed along linear habitats such as railway lines, although alternatively, it has been suggested it was accidently introduced with rape seed of Argentinian origin. Another possible source of the weed in Saskatchewan suggests it arrived as a contaminant of farm seed or hay originating from the United States (Desrochers et al. 1988). Individual plants of C. nutans produce large numbers of seeds that germinate very readily, dormancy being as short as twelve days and the very spiny leaves deter grazing, factors that lead to the invasive success of the weed (Desrochers et al. 1988).
Flowering reproduction
C. nutans flowers from May to August, the capitula emitting a quite strong musky or almond-like odour, especially during sunny weather (Salisbury 1964; Desrochers et al. 1988; Perring & Walters 1989). The perfect (bisexual) flowers are mainly outbreeding, being insect pollinated by bees, wasps, butterflies and moths. The mean number of flower-heads per plant is around 20, although large plants may produce twice this number. Each capitula produces between 130 and 300 fruit achenes (ie single seeded dry fruits), each with its characteristic parachute pappus of hairs. The long white parachute hairs of the fruit pappus are minutely toothed, but not feathery as in Cirsium thistles. Thus the average seed production calculated by Salisbury (1964) in his British study was 4,000 per plant. In a Canadian field study carried out in Nebraska, where the species is a serious, patch-forming invasive alien, each plant produced an average of between 10,000 and 11,000 achenes (McCarty 1982). Although obviously adapted for wind dispersal, study shows the vast majority of achenes land near the parent plant (ie within 50 m) and less than 1% travel more than 100 m (Smith & Kok 1984).
The soil seed bank survey of NW Europe published just four estimates of C. nutans buried seed longevity, which proved inconclusive since every one was different and covered the spectrum equally from transient to long-term survival (Thompson et al. 1997). Several studies in Canada, however, suggest seed survival remains high over several years, with little loss of viability after ten years (Kok 1978; Roberts & Chancellor 1979; Burnside et al. 1981).
Fermanagh occurrence
There is just the one Fermanagh record, as detailed above, so it has not been seen for over half a century in this land-locked, but not very inland VC. While it certainly is a distinctive thistle, yet the existence of the solitary Fermanagh record speaks highly of the keen powers of observation of Meikle and his co-workers carrying out their flora survey in the 1947-57 period, that they noticed such an extremely rare, casual species. No one else has seen it since.
British and Irish occurrence
In Ireland, apart from the area about Galway Bay, and, as shown in the New Atlas map as a spate of recently recorded hectads in and around Co Carlow (H13), C. nutans is a very rare and thinly scattered plant. This is especially so in the north of the island. C. nutans has long been regarded as a casual, introduced, seed contaminant, usually only fleetingly present in reseeded fields, or in disturbed, artificial habitats and, even then, mainly occurring near coasts (F.H. Perring, in: Preston et al. 2002).
In England and Wales, C. nutans is accepted as indigenous and it is widespread and locally common, at least in southern areas of England, Wales and SE Scotland to the Firth of Forth. Beyond this, it is thinly and widely scattered, and is generally considered a casual introduction (F.H. Perring, in: Preston et al. 2002).
European and world occurrence
C. nutans belongs to the Eurosiberian temperate phytogeographical element and is widespread in Europe up to 67oN in Scandinavia and Finland, around the Mediterranean and in N Africa, although it is absent from the Mediterranean isles with the exceptions of Sicily, Sardinia and Corsica. It stretches eastwards to Turkey, E Himalaya, India, Pakistan, Siberia and China. It is also widely introduced to S Korea, SE Australia, New Zealand, N America and Argentina (Hultén & Fries 1986, Map 1859).
Names
The genus name 'Carduus' is not Greek as genus names usually are, but rather it is Latin, and it is the classical name for a thistle (Gilbert-Carter 1964; Stearn 1992). The Latin specific epithet 'nutans' from 'nuto' meaning 'nod' is 'nodding', an obvious reference to the very characteristic hanging capitula (Gilbert-Carter 1964).
There are two English common names that are widely used, 'Musk Thistle' and 'Nodding Thistle', the former referring to the often faint, but pleasant musky or almond-like scent given off by the flowers, and the second to the obvious hanging capitula. Grigson (1955, 1987) adds three more names, 'Buck Thistle', 'Queen Anne's Thrissel' and 'Teaser' from places as far apart as Berwickshire in Scotland and Somerset. He does not bother to explain derivations for any of them. Prior (1879) add 'Scotch Thistle' to the list of names, this being the national badge of Scotland. He explains that the thistle can be of any kind, and it was adopted, it is claimed, because a night attack by a Danish army was betrayed by one of its bare-footed soldiers treading on a thistle in the dark. The elegant habit of the Musk Thistle led artists to choose it for the emblem. Britten & Holland (1886) add 'Bank Thistle' to the list of English names, again without explanation.
References
Hultén & Fries 1986; Preston et al. 2002; Sell & Murrell 2006; Melderis & Bangerter 1955; Garrard & Streeter 1983; Perring & Walters 1989; Grime et al. 1988, 2007; Desrochers et al. 1988; Salisbury 1964; Britten & Holland (1886); Prior (1879); Grigson (1955, 1987); Gilbert-Carter 1964; Stearn 1992; Kok 1978; Roberts & Chancellor 1979; Burnside et al. 1981; Thompson et al. 1997; Smith & Kok 1984; McCarty 1982; Harris (1984)