- Name also: Spiny Plumeless Thistle, Bristly Thistle, Broad-winged Thistle
- Family: Daisy Family – Compositae, subfamily Carduoideae
(formerly Aster Family – Asteraceae)
- Growing form: Biennial herb.
- Height: 30–120 cm (12–50 in.). Stem branched, winged, tomentose, spined. Spines up to 5 mm (0.2 in.) long, strong, yellowish.
- Flower: Flowers 2.5–3.5 cm (1–1.4 in.) wide, single flower-like capitula surrounded by involucral bracts. Capitulum lacks ray-florets; disk florets light reddish violet–purple (rarely white), tubular. Stamens 5. Gynoecium composed of 2 fused carpels. Involucre hemispherical, involucral bracts overlapping in many rows, linearly lanceolate, spine-tipped. Capitula 2–3 in a dense cluster or sometimes solitary. Pedicels usually very short, winged and spiny, capitula erect.
- Leaves: Alternate. Blade pinnately lobed, rigid, spined, haired along green veins underneath, becoming glabrous on top.
- Fruit: Flattish, slightly curved, glabrous, with glands, shiny, olive green, 3–4 mm (0.12–0.16 in.) long achene crowned by a pappus of branched, feathery, 11–13 mm (0.44–0.52 in.) long hairs.
- Habitat: Dumps, mill areas, beside railway tracks, roadsides, ballast soil deposits. Calciphilous.
- Flowering time: July–September.
The success of the huge family of capitulum-flowered plants is based on its diversity. One direction of development is thistle-like plants, which protect themselves from hungry predators – and nowadays also people – with cruel-looking spines. Thistles give us a hint about these plants’ diverse defence systems. In Finland the pressure of herbivores is substantially smaller than it is on the mountain slopes of Mediterranean countries with their herds of sheep and goats, so thistles are less polymorphic here. Thistles however require herbivores – or humans – to keep the habitat open as they cannot survive for long in overgrown or grassy places.
Welted thistle is one of the prickliest thistles in Finland: its spines are found at the edges of the wings and amongst the pedicel’s white woolly hairs, all strong, straight and sharp-pointed, sometimes almost a centimetre (0.4 in.) long. The species isn’t established in Finland, but it grows casually on ballast soil deposits around harbours and near mills and railways. Most plants can be found in southern Finland, but it can also be found in harbour towns along the Gulf of Finland as far north as Oulu. Welted thistle is already established in sandy places in the south of Sweden and in Denmark, although it is rare.
Welted thistle’s spines are probably its best identification marker: more common curled thistle’s (C. crispus) leaves can be grasped without gloves. The species can be differentiated according to their colour: welted thistle is more clearly green than curled thistle, which is densely light-haired on the underside of its leaves.