Plant of the week – September 27th 2021 – The Scottish Thistle

In Search of the Scottish Thistle

Most thistles are now busy releasing their thistle down (or botanically speaking their plumose pappi), so you may think this plant-of-the-week blog is a bit late in coming. On the other hand, over the summer months you will have had a chance to observe the plants in their full green and purple glory, to identify the 22 or so species (not to mention the hybrids) which according to Stace (1997) all bear the English epithet of ‘thistle’, and to ponder which of these is actually our National Flower.

While England has its rose (Rosa canina), Ireland its shamrock (Trifolium dubium) and Wales the daffodil (Narcissus) or leek (Allium porum), Scotland’s national floral emblem is one of several thistles.

In my capacity as a garden guide at the Royal Botanic Garden Edinburgh, I am often asked to show tourists the Scottish thistle, so which one should I show them? There is a spectacular plant of Onopordum acanthium (commonly known as the cotton thistle) in the Garden’s herbaceous border, but this species is not native to Scotland. So, should I show them that, let them take selfies against it and leave them happy but misinformed? Or do I underwhelm them with our own native Cirsium vulgare, the spear thistle, a rogue weed with spear-like leaf tips and involucral bracts that occasionally escapes the gardener’s hoe. The spear thistle is one of 10 Cirsium species in Britain, but the genera Carduus, Cynara, Echinops and Silybum are also commonly named as ‘thistles’. Some of these do not have the look of our emblem while still meriting the name ‘thistle’, but that still leaves about as many which could be contenders for the title.

Dickson and Walker (1981) in their definitive paper on this subject list 11 species (in alphabetical order) which have been used to model the emblem for various Scottish artefacts:

Carduus nutans (Musk Thistle): this is unlikely as it is rare (Figure 3).

Carlina acaulis (Stemless Carline Thistle): unlikely, not native

Cirsium acaule (Stemless Thistle): Does not occur north of Yorkshire.

Cirsium eriophorum (Woolly thistle): Not native in Scotland, though occurs as a casual in Edinburgh.

Cirsium helenoides= C. heterophyllum (Melancholy thistle): Native and widespread (Figure 4)

Cirsium vulgare (Spear Thistle): Native and common (Figures 1 and 5).

Cyanara cardunculus (Cardoon Thistle): Cultivated only.

Echinops ritro (Globe thistle): Cultivated but may be found as escapes.

Onopordon acanthium (Cotton Thistle): Non-native, cultivated, occurs as a casual (Figure 2).

Onopordon arabicum: non native and not even casual.

Silybum marianum (Milk Thistle) Not native.

Of those, the two most likely contenders for our National Flower are Cirsium vulgare (Figure 1) and Onopordum acanthium (Figure 2), the very ones I was left swithering about in my RBGE tours. Silver coins issued by James III in 1470 were the first to bear the thistle emblem. The species represented on these was Cirsium vulgare identified by Dickson and Walker (1981) by the taller, tapered involucre and very protuberant flowers. However, the coins issued in later Stewart times bear the squatter capitula that resemble Onopordum acanthium, probably modelled on plants introduced from France to Scottish palace gardens in mid to late sixteenth century possibly by Mary of Guise, the wife of James V, who was known to be keen to promote the Auld Alliance and all things French.

There is a very appealing, if apocryphal, story that the thistle became the emblem of Scotland because it protects us from invaders. In the eleventh or twelfth century the country was prone to invasion by gangs of sea-faring Danes, who in the dead of night, homed in on settlements which they spotted from the inhabitants’ lit fires and lights. They were shoeless of course as many people were in those days, and when one of the intruders stepped on a prickly thistle, he let out a yelp waking up the locals who promptly despatched the invaders. We have a motto to commemorate the event: “Nemo me impune lacessit”, “No-one harms me without punishment” but more commonly translated in Scots as “Wha daurs meddle wi me”.

Now, the thistle species that the invader stepped on could not have been Onopordum, because it had not been introduced yet, nor could it have been one of the English thistles that is not native North of Yorkshire. Cirsium vulgare, with its deadly-sharp armoury, is surely the likeliest contender for the Scottish thistle.

All the contenders mentioned above belong to the family Asteraceae (Compositae as was), but more recently an Eryngium, an alien interloper from the Apiaceae, has been trying to steal the Scottish National Flower title. Our native Eryngium maritimum is the sea holly, but it is not that which has been adopted as the florists’ Scottish thistle, but Eryngium planum, which is often made up into buttonholes for Scottish weddings. It is now erroneously branded as the Scotch thistle – a bit like the Scotch Whiskey which comes from the US. My botanist husband was not impressed when presented with an Eryngium buttonhole on the occasion of our son’s wedding – especially as it was chosen to celebrate the said son’s Scottish provenance. I told this story to a group of visitors I was guiding round the Botanic Garden Edinburgh, and a few minutes later they gleefully spotted the very same Eryngiums in the lapels of passing wedding guests.

The Cirsium vulgare flower is rated 6^th in the UK flora for nectar production per unit cover per year (kg of sugar/ha/year), (AgriLand, 2011-2012).   Interestingly, this league table is topped by the Marsh Thistle (Cirsium palustre).  Both species are the favourite nectar sources of the fritillary butterflies (pearl-bordered fritillary, small pearl-bordered fritillary, high brown fritillary and dark green fritillary), (Butterfly Conservation, 2005). Many photographs of thistles show a pollinator calmly sucking from the many florets (e.g. Figure 5 and also the frontispiece of our BSS News of March 2021).

Cirsium vulgare as the BSBI map shows is very common in the UK but, being native, it is not classed as invasive. It is however, one of the five ‘top’ weeds, classed as ‘injurious’ under the Weeds Act of 1959. This gives the Secretary of State the right to serve an enforcement notice on the occupier of land on which ‘injurious’ weeds are growing (DEFRA, 2009). In the US it is classed as a moderately invasive alien (Edwards, 2021).

The plants are biennial or occasionally annual. The leaves are deeply lobed; the lobes are spear-tipped. The flower heads (capitula) consist of an involucre that is 2.5-4 x 2-5 cm, tapers towards the top and bears numerous spear-tipped bracts. The florets are uniform with no division into ray and disc florets. The seeds are 5 mm long, with a downy pappus, which assists in wind dispersal. As in other species of Cirsium (but unlike species in the related genus Carduus), the pappus hairs are feathery with fine side hairs. Propagation is by seed. The plant has a tap root, but no runners.

Now in mid- September the thistle’s work is done, but the seeds will forge ahead with vigour for another year. The poem Thistles by Ted Hughes ends with:

“Then they grow grey like men.
Mown down, it is a feud. Their sons appear
Stiff with weapons, fighting back over the same ground.”

References:

AgriLand (2011-2012). The Agriland Project (www.agriland.leeds.ac.uk/) is a partnership between The University of Leeds, University of Reading, University of Bristol, Defra’s Food and Environment Research Agency (FERA), and Natural Environment Research Council’s Centre for Ecology and Hydrology.

Butterfly Conservation (2005). Bracken for butterflies. https://butterfly-conservation.org/sites/default/files/habitat-bracken-for-butterflies.pdf (accessed 18 September 2021).

DEFRA, 2009. Enforcing the Weeds Act 1959. https://www.welhat.gov.uk/media/3088/DEFRA-information-on-weeds/pdf/Weed_Info_Sheet_Defra.pdf?m=634176376360000000 (accessed 18 September 2021)

Dickson, J & Walker, A. (1981). What is the Scottish thistle? Glasgow Naturalist (20)2): 1-21.

Edwards, P. (2021). Familiar faces: discovering similar and native plants of Scotland and California. BSS News, No 116, pp 50-55.

Stace, C. (1997). New Flora of the British Isles (2^nd ed.), CUP.

Maria Chamberlain