Brown knapweed |
Flower head, involucre and leaf of the brown knapweed
| Centaurea jacea s. str. L.: | |
| Blooming period: | June–September |
| Height: | 30–120 cm |
| Flowers: | in heads, Ø of the heads 25–32 mm, stamens: 5, styles: 1 |
| Ray florets: | missing |
| Disc florets: | red violet |
| Calyx: | missing or transformed into bristles |
| Stem leaves: | alternate, linear to lanceolate |
| Basal leaves: | stalked, lanceolate to elliptical or irregularly pinnatifid, missing at the flowering season |
Plant perennial, herbaceous, with short taproot.
Stem erect or ascending, strongly or slightly branched, grooved, thin, shaggy haired, tomentose or coarse-haired, soon bare.
Stem leaves alternate. Lower leaves stalked, oblong-elliptic, sometimes pinnatilobate or only slightly serrated. Leaves decreasing upwards in size, linear-lanceolate, sessile, entire or toothed.
Flower heads usually solitary or a few ones in corymbose inflorescences on stalks that are sometimes thickened below the flower head and equipped with a bract. Receptacle flat and bristly.
Phyllaries in 6–8 rows, tightly imbricated. The outer ones are ovate to lanceolate, glossy dark brown, with wide membranous margins and with fringed, white or brown appendages. The middle and inner phyllaries are slotted, irregularly toothed, lobed or entire. Involucre 15–18 mm in diameter, bell-shaped or oval to hemispherical.
The flower heads consist exclusively of purple tubular florets, at the base without chaffy leaves. Outer petals more or less prolonged, but mostly extended conspicuous, sterile, zygomorphic, 5-toothed. Inner bracts almost radiate, hermaphrodite, male or female, 5-toothed, 15–18 mm long.
After pollination by bees, bumblebees or butterflies, the inferior ovary an up to 3 mm long nut fruit (achene), which is finely hairy, elongated, flattened and without a pappus or with few bristles at the apex. Plants very diversiform!
In Germany there are three accepted subspecies:
Centaurea jacea ssp.
timbalii: branched from the base, leaves soft and
long hairy.
Centaurea
jacea ssp. decipiens: leaves soft and
long hairy, with small flower
heads.
Centaurea jacea ssp. microptilon:
highly branched,
outer florets not extended, bracts with small, thin appendages.
Centaurea jacea may form hybrids with C. diffusa, C. nemoralis, C. nigrescens and C. stoebe
| Floral formula mostly: |
| *–↓ K0 oder K=bristles [C(5) A5(connate)] G(2) inferior |
Occurrence:
Meadows
and roadsides, embankments. Prefers dry and loamy soils.
Distribution:
Eurasia,
introduced in North America.