Centaurea americana

American knapweed ( Plectocephalus americanus)

The American knapweed ( Plectocephalus americanus, Syn. Centaurea americana Nutt ) is a plant of the genus Plectocephalus in the sunflower family ( Asteraceae).

Features

The American knapweed is an annual plant that reaches the plant height of 30 to 200 centimeters. The upright stem is simple or little branched. The change-constant and seated or winged - stalked leaves are glabrous or rough, glandular- dotted, narrowly ovate to lanceolate and 8 to 20 inches long. The upper leaves are entire, the lower toothed.

The wide hemispherical flower basket shell has a diameter of 3 to 5 centimeters. The Hüllblattanhängsel are straw- colored, not out continuously and comb-shaped fiederteilig with about 15 sections. The cup -shaped inflorescence has a diameter of generally 4 to 8 ( 3-10 ) centimeters. The tubular flowers are pink or purple, rarely white. At the edge of the disc florets are ungeschlechtig, sterile, zygomorphic and somewhat enlarged, 35 to 50 mm long. The inner tubular flowers are hermaphrodite, fertile, radial symmetry, usually lighter and 20 to 25 mm long.

The flowering period extends into Central Europe from July to August, otherwise as early as February.

The gray - brown to black achenes are 4-5 mm long, glabrous or with white hairs near their base. The pappus consists of stiff, unequal, 6-14 mm long bristles.

Occurrence

The American Knapweed comes in the warm central North America from northeastern Mexico (Chihuahua, Coahuila, Nuevo León, San Luis Potosí, Tamaulipas ) to the following U.S. states: Arizona, Arizona, Oklahoma, Texas, Missouri and Louisiana before. It grows in prairies, Grass countries, fields, open forests and in disturbed habitats at altitudes 0-2100 meters. This type tends to run wild ( invasive plant).

Use

The American knapweed is rarely used as an ornamental plant for summer borders and as a cut flower. It is in culture at least since 1824. There are some varieties whose flowers dark purple or white.

Documents

• David J. Keil: Plectocephalus in the Flora of North America, Volume 19, page 176: Plectocephalus americanus - Online. (English )
• Eckhart J. Hunter, Friedrich Ebel, Peter Hanelt, Gerd Müller, K. (ed.): Rothmaler Exkursionsflora of Germany. Volume 5: Herbaceous ornamental and useful plants. Spektrum Akademischer Verlag, Berlin Heidelberg 2008, ISBN 978-3-8274-0918-8.