- Height: 30–80 cm (12–32 in.). Many-branched. Stem erect, branchless–short-branched at top, underside of capitulum thick, sparsely short-haired, slightly rough.
- Flower: Single flower-like 3–4.5 cm (1.2–1.8 in.) capitula surrounded by involucral bracts. Capitula flowers purplish, ray-florets neuter, obliquely funnel-shaped, tip lobed; disc florets tubular. Stamens 5. Pistil of 2 fused carpels. Involucre barrel-shaped, involucral bracts overlapping in many rows, usually light reddish brown, centres darker, appendage membranous, roundish, later tearing into lobes. Capitula usually solitary, terminating stem branches.
- Leaves: Alternate, lower stalked, upper stalkless, slightly decurrent. Blade (broadly) lanceolate, with entire margins–sparsely toothed, sometimes lowest shallowly lobed, with short, greyish hairs.
- Fruit: Elliptic, slightly flattened, light brown achene, tip sometimes with few bristles.
- Habitat: Dry meadows, pastures, forest margins, wasteland, banks.
- Flowering time: July–August.
Brown knapweed is a beautiful member of the Daisy family that grows on sloping meadows and banks in southern and central Finland. The funnel-shaped ray-florets, which are the most eye-catching part of the capitulum, are without gender, meaning that they have no stamens or pistils. Their task is to advertise the flower to insects and lead them to the small, tubular disc florets so that they can pollinate them and allow cypselas to develop. Knapweeds are particularly favoured by bees, but day butterflies and flower flies are also attracted to their bluish violet flowers. People are also fond of knapweeds, and the genus includes many ornamentals. It is worth experimenting with transplanting varieties that thrive in Finland as they often take to their new habitat and grow and flower strongly.
Finland’s established flora includes only 1% of the species in genus _ Centaurea_ – around four or five species – although several more grow casually in the wild as escapes. Of the knapweed plants that have taken root in Finland, three stand out with their purple flowers: brown knapweed, wig knapweed (C. phrygia) and greater knapweed (C. scabiosa). Greater knapweed’s once or twice-lobed leaves differentiate it from its close relations, and the tips of the capitula’s involucral bracts don’t divide into a distinctly separate appendage like the other two species: rather it surrounds the scale’s green basal part in the shape of a narrow curve. Brown knapweed’s appendage is brown, paper-thin and only partly lobed. Wig knapweed looks very similar but its appendage is usually blackish and beautifully ciliately fringed. Although the species have similar demands regarding habitat, they do not often grow together because brown knapweed grows mainly in the west and south-west while wig knapweed favours the east of the country. Both species are old established aliens which grow around inhabited areas and disappear if the vegetation returns to its original state, i.e. forest.