Lesser knapweed |
Habit, flower head, involucre and leaf of the lesser knapweed
| Centaurea nemoralis Jord.: | |
| Blooming period: | July–September |
| Height: | 30–100 cm |
| Flowers: | in heads, Ø of the heads 20–30 mm, stamens: 5, styles: 1 |
| Ray florets: | missing |
| Disc florets: | purple |
| Calyx: | transformed into bristles |
| Stem leaves: | alternate, linear to lanceolate |
| Basal leaves: | stalked, lanceolate to elliptic, simple to lobed, missing at the flowering season |
Plant perennial, herbaceous, with a strong taproot.
Stem erect to ascending, usually highly branched, grooved, cobwebby, soon bare.
Stem leaves alternate. Lower leaves stalked, oblong-elliptic, sometimes slightly serrated or pinnatilobate. Leaves decreasing upwards in size, linear-lanceolate, sessile, entire, dentate or with narrow lobes.
Flower heads solitary or a few ones in corymbose inflorescences on stalks that are clearly thickened below the flower head and equipped with a bract. Receptacle flat and bristly.
Phyllaries in 6–8 rows, tightly imbricated. The outer and the middle ones are ovate to lanceolate, glossy dark brown to black, margins with brown and comb-shaped appendages.
The inner phyllaries are irregularly toothed or lobed. involucre ovate, up to 15 mm in diameter. Comb-shaped appendages are much longer than the phyllary is wide without appendage.
The flower heads consist exclusively of purple tubular florets, at the base without chaffy leaves. Outer petals not extended and not sterile. All florets more or less radiate, hermaphrodite, 5-toothed, 15–18 mm long.
After pollination by bees, bumblebees or butterflies, the inferior ovary forms an up to 3 mm long nut fruit (achene) which is finely hairy, elongated, flattened and without a pappus or with many irregular, up to 1 mm long, blackish bristles at the apex. Plants very diversiform!
Centaurea nemoralis may form bastards with C. jacea, C. phyrgia and C. pseudophyrgia.
| Floral formula: |
| * K=bristles [C(5) A5(connate)] G(2) inferior |
Occurrence:
Forest
edges and roadsides, on rails, ruderal areas. Prefers slightly cool,
moist, acidic and not too nitrogen-rich locations.
Distribution:
Europe,
introduced in North America.