28 species in the Collins Flower Guide have the word “thistle” in their name. They are all members of the large and often confusing family of Asteraceae. Sixteen of them are classed as true thistles, and at least ten of these are native species. For the purposes of this spotlight, we’re going to concentrate on the three (and a half) true thistles found at St Nicks: Creeping Thistle Cirsium arvense, Spear Thistle Cirsium vulgare, and Welted Thistle Carduus crispus.
It isn’t hard to tell them apart. A full-grown Spear Thistle is an impressive plant capable of growing to 150cm, with spines on its stems and spiky bluish-green leaves ending in a distinctive, long, spear-like point. It’s a biennial – growing in year one, flowering in year two, seeding itself, then dying back. The flowers come in clusters of up to three, with large, rounded heads and a dense tuft of purple florets. New plants start out as beautifully arranged rosettes almost flat to the ground, particularly attractive when outlined with a touch of frost.
Creeping Thistle is a perennial – the same plant can keep on coming up year after year. The leaves are brighter green than Spear Thistle, and have lots of relatively small but very sharp prickles. The flower heads are much smaller and more elongated, and the florets are a rather muted light purple. One of its most distinctive characteristics is the lack of spikes on the stem. If you need to pull one up, get hold of it in the centre low down, but it’s still safest to wear tough gloves.
Welted Thistle, another biennial, can grow as tall as Spear Thistle but is a more slender plant. Its flowering heads are rounded, with rich purple florets, and the stems have continuous spiny wings that stop just below the flower heads. We’re keeping an eye on the St Nicks Welted Thistles because some of them seem to be less prickly than others, and they are known to hybridise with the less common Musk Thistle, Carduus Nutans. We once, probably mistakenly, thought we’d found one of these…
All three species produce fluffy seed heads (“thistle-down”) from which individual seeds fly off on little “parachutes”. Creeping Thistle has another weapon in its armoury that makes it dreaded as a farmland weed. The fact that it can keep coming up year after year gives it a head start. The range of the floating seeds on a good breeze enables it to spread over a large area – but it also propagates itself by underground rhizomes so that it can rapidly dominate its immediate locality.
Our three species all like rough grassland on fertile soil, and will rapidly move into neglected fields and allotments. Obviously we don’t want them to take over the meadow. That means we need to keep an eye open for young Creeping Thistles before they start to spread. Otherwise, the cutting and planting strategies that we use to reduce soil fertility and restrict coarse grasses will limit the biennial species and in time make the area less attractive to thistles. Welted Thistle will grow happily on clay soil in less open areas so there’s always the possibility that it might be helping to make our capped areas more hospitable to smaller plants.
So what good are thistles? If we don’t want them in the meadow, do we want them anywhere else?
The ones regularly listed in modern herbals are introduced species. Native ones were used in the middle ages to make salves but seem to have dropped out of use long ago. Now, it seems that they are being reassessed for medically useful properties. Winnie-the-Pooh’s friend Eeyore ate them, but grumbled about it. The core of a thistle head can apparently be eaten like an artichoke heart (a related species) as can tender stems, but the consensus of foraging chatrooms seems to be that it isn’t worth the bother. On the other hand bees and butterflies love the flowers, and Goldfinches feed enthusiastically on the seed heads. Their scientific name Carduelis carduelis can be traced back to the Roman writer Pliny, and just means “associated with thistles”. Carduus thistles are also the food plant of the Painted Lady butterfly. A much less well known species dependent on Creeping Thistles is a fly, Urophora cardui, which induces elegantly shaped galls in the stems where its larvae develop and feed.
Although there are other candidates and plenty of argument, Spear Thistle looks likely to be the reality behind the celebrated Scottish Thistle – proud national emblem and origin of the motto Nemo me impune lacessit, “Nobody wounds me unpunished”. The legend says that during a night attack an invading Dane trod on one, and his howl of pain woke the defending Scots in time. So in the Victorian language of flowers, thistle means retaliation. But the Scots connection may go back much further to Celtic tradition where the thistle (again not clear exactly which one) symbolises courage, loyalty and resilience. Not a bad emblem!
 Plants in this group, which includes Dandelions and Daisies, have what look like individual flowers, but are actually clusters of florets each of which has everything it needs to reproduce itself. Pull all but one “petal” out of a thistle head and it can still produce a seed.