True Thistles
What are they?
Thistles will be familiar to everyone and few people cannot have inadvertently brushed past one (or sat on one at a picnic!) and felt its wrath! These are members of the large Asteraceae family and this is apparent from the flowers, which typically consist of a bundle of few to many, small florets, bundled together to form a compound flowerhead. In most species, the leaves, stems and outer parts of the flowerheads all carry often formidable-looking spines, but there are also some with less fierce armament.
Where are they found?
There seems to be a thistle for every occasion, with most habitats holding one or two species, so habitat can help a little towards identification. But most species will be found in disturbed, nutrient-rich habitats or in permanent grasslands.
Identification
The shape of the leaves and the arrangement of their spines is important, while the presence or absence of spiny wings on the stems can also be useful. As with most members of the Asteraceae, the appearance of the phyllaries - the green, outer part of the flowerhead - is important and these should always be checked. Note that most species can sometimes produce plants with white flowers, though they seem to be particularly frequent in Marsh Thistle.
Creeping Thistle Cirsium arvense
Native and found commonly in a wide range of habitats, but usually disturbed or nutrient-rich soils. Flowers late June to September. A persistent and deep-rooted perennial that forms spreading colonies of close-growing, upright stems. Flowers a paler lilac colour than most thistles. Phyllaries tightly pressed to the flowerhead with just the prickly tips bent outwards.
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Spear Thistle Cirsium vulgare
Native and found commonly in a wide range of habitats, but usually disturbed or nutrient-rich soils. Flowers late June to September. A strong-growing, stout and often multi-branched species with long, stout spines. Flowerheads large and form perhaps the 'classic' thistle. Phyllaries curved and spreading, with long, sharp, spiny tips.
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Marsh Thistle Cirsium palustre
Native and found commonly in a wide range of habitats on damp soils, especially coastal freshmarsh and wet areas in shady places and woodland. Flowers late June to September. Plants form dense-leaved, basal rosettes before sending up a flowering stem, with leaves usually heavily purple-tinted. Flowers deep purple but occasionally white. Phyllaries tightly pressed to the flowerhead with just the prickly tips bent outwards.
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Dwarf Thistle Cirsium acaule
Native. Common in open areas of short, dry grassland in Breckland, but uncommon and thinly scattered elsewhere. Flowers July to September. A small plant, forming a flat rosette of very spiny leaves, topped with short-stalked or more or less stemless flowerheads. Phyllaries tightly pressed to the flowerhead with just the prickly tips bent outwards.
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Meadow Thistle Cirsium dissectum
Native. A plant of acid to neutral wetlands, frequent on Broadland and along the Little Ouse but rare elsewhere. Flowers June to August. A delicate thistle with long, upright, spineless flower stems. Leaves with small, relatively soft spines along the margins. Phyllaries tightly pressed to the flowerhead with just the prickly tips free and pointing upwards.
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Woolly Thistle Lophiolepis eriophora
(Cirsium eriophorum) Native in grassy places on chalky soils. Very rare in West Suffolk and absent from Norfolk, but frequent on the chalky soils of south Cambridgeshire. Flowers July to September. An impressive plant with fingered leaf lobes terminating in spiny tips and very large flowerheads. Much of the plant os covered in dense, white-woolly hairs. Phyllaries curved outwards, strongly spine-tipped and mostly hidden amongst woolly hairs.
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Musk Thistle Carduus nutans
(Nodding Thistle) Native. Common and widespread on lighter, sandy or chalky soils but largely absent from the heavier clays. Flowers May to August. A very spiny thistle with multiple stems arising from a leafy basal rosette. Flowers rich purple, the heads distinctive as they nod over to one side on maturity. Phyllaries wide-spreading, often curving backwards and sharply spiny.
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Welted Thistle Carduus crispus
Native. Found in grassy places throughout the region on richer soils along the main river valleys but absent from lighter and wetter soils. Flowers late June to August. Resembles some of our commoner thistles but has smaller, more clustered heads than those of Spear Thistle and larger, more spiny heads than Marsh Thistle. Phyllaries spreading and sharply spiny and with whispy strands of cobweb-like hairs.
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Slender Thistle Carduus tenuiflorus
Native. Largely a southern species of coastal grasslands which is common along the flatlands of coastal Essex and Suffolk but is almost absent from Norfolk except around Breydon Water. Occasionally appears elsewhere as an introduction from various seed sources. Flowers June to August. A slender, very spiny plant often with a greyish cast to the leaves and stems. Flowers relatively small, pale pink to whitish in colour. Phyllaries spreading, broad-based and spiny.
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Cotton Thistle Onopordum acanthium
Introduced, probably by the Iron Age. Widespread but most common on light sandy soils, especially in the Breckland, the Suffolk Sandlings and around Norwich. Flowers late June to September. An imposing plant which may grow to three metres in height. Very distinctive, with dense, white-cottony hairs smothering all parts of the plant except the florets. Stems strongly winged.
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Milk Thistle Silybum marianum
Introduced from mainland Europe. Scattered throughout the region and perhaps increasing in grassy places and on roadsides. Flowers June to August. Spreads to form often dense patches of many plants and may grow to over two metres in height. Easily recognised by the white lines that trace the veins on the leaves. Phyllaries very distinctive, held tightly at their bases but wide-spreading at the tips, often with formidable spines at their tips.
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Purple Milk Thistle Galactites tomentosus
Introduced from mainland Europe. Occasionally grown as a garden ornamental or perhaps as a birdseed contaminant and noted in Norfolk and Cambridge. Flowers June to August. A distinctive, usually well-branched plant with white leaf-veining and showy flowerheads.
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Cardoon Cynara cardunculus var. cardunculus
Introduced from mainland Europe as an ornamental. Uncommon but occasionally found as a relic of cultivation or garden throw-out on rough ground and roadsides. Flowers July to September. Plants may reach two metres or more in height with leaves of over a metre in length. Plants grey-hairy and flowerheads large with bluish-purple florets. The stiff phyllaries are usually spine-tipped. Globe Artichoke (below) is a cultivated variety of Cardoon.
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Globe Artichoke Cynara cardunculus var. scolymus
Introduced from mainland Europe as a culinary plant. Uncommon but occasionally found as a relic of cultivation or garden throw-out on rough ground and roadsides. Flowers July to September. Plants may reach nearly two metres in height with leaves of over a metre in length. Plants greenish to grey-hairy and flowerheads large with bluish-purple florets. The stiff phyllaries are spineless and it is the bases of these that are cooked or pickled and eaten. The Globe Artichoke is a cultivated variety of Cardoon.
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Common Carline Thistle Carlina vulgaris
Native. Found in grassy places on low-nutrient, sandy or chalky soils, mostly on the Norfolk and Suffolk coastal sands and dunes and in Breckland, then on chalk in Cambridgeshire. Flowers July to October. A small plant, to no more than 60cm in height. Flowerheads have a ring of straw-coloured, petal-like bracts that stiffen and remain attached throughout the winter, long after the flowers have set seed. The florets themselves are yellowish in bud, opening with dark purple petals. Phyllaries intricately divided into narrow fingers with spiny tips.
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Cabbage Thistle Cirsium oleraceum
Introduced. A rare casual, recorded less than 10 times as a short-lived garden escape or throw-out. Flowers July to September. Mostly a soft-leaved species with single small spines at the tips of the leaf lobes. Phyllaries hairless and upright, the outer few with a small spine at the tip. Flowers pale yellowish-white.
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