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Greater Knapweed

Centaurea scabiosa

  • Family: Daisy Family – Compositae, subfamily Carduoideae
    (formerly Aster Family – Asteraceae)
  • Growing form: Perennial herb. Rootstock strong.
  • Height: 30–100 cm (12–40 in.). Stem branching from top, bristly.
  • Flower: Single flower-like 3–4.5 cm (1.2–1.8 in.) capitula surrounded by involucral bracts. Capitula flowers violet red (occasionally pink or white), ray-florets neuter, obliquely funnel-shaped, tip lobed; disc florets tubular. Stamens 5. Pistil of 2 fused carpels. Involucre almost spherical, involucral bracts overlapping in many rows, basal part green, tip roundish, brownish black, ciliately fringed. Capitula solitary, terminating stem branches.
  • Leaves: Alternate, stalked. Blade dark green, slightly leathery, irregularly 1–2 times lobed (occasionally quite entire), lobes narrow.
  • Fruit: Flattish, light brown, short-haired, 4.5–5 mm (0.18–0.2 in.) long achene, tip with 4–5 mm (0.16–0.2 in.) long, brownish gray bristles.
  • Habitat: Dry banks, meadows, roadsides, pastures.
  • Flowering time: July–September.

Greater knapweed is probably originally from the Russian steppes. Finnish plants seem to have a few different origins: stands are linked in one way to old agricultural practice, and in another way are formed of more recent arrivals by road and rail. Greater knapweed grows mainly in southern Häme, and its habitat stretches from there to the Lohja–Vihti area and north-east towards Mikkeli. More sparse and compact stands can also be found on the Åland Islands and southern Savo, but it is very rare in most of southern and central Finland. Its stands are mainly around inhabited areas and places with a lot of traffic. Its achenes do not have proper flying hairs so they cannot float on the wind. They remain in the capitula involucres, and are held aloft above the snow by the stems which remain rigid throughout the winter. Small birds also feed on them, spreading the seeds.

The large ray-florets on greater knapweed’s capitula make it look very ornamental, and the species is also cultivated in gardens. The ray-florets have no functioning stamens or pistils – their only task is to attract insects to the disc floret in the centre of the capitula where fertilization will create seeds. Apart from being an ornamental, greater knapweed has also sometimes been used to treat scabies and other skin complaints, and this is the root of its scientific name scabiosa. The plant could also be boiled to yield dye.

With its lobed leaves, greater knapweed bears a slight resemblance to red-flowered thistles (Cirsium), although its lack of spines makes it easy to tell apart. Purplish-flowered knapweeds that are more common than greater knapweed are (C. jacea), which is slightly smaller, and wig knapweed (C. phrygia), which has entire leaves. Additionally, the involucral bracts that protect the flowers are sharply constricted into two parts (a narrow ‘waist’ between the tip and base), of which the details on the tip of the appendage are important identifying marks. The tip of greater knapweed’s bract has a narrow ciliate edge.

Other species from the same genus
Other species from the same family

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