American knapweed
| American knapweed | ||||||||||||
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American knapweed ( Plectocephalus americanus ) |
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| Plectocephalus americanus | ||||||||||||
| ( Nutt. ) D.Don |
The American knapweed ( Plectocephalus americanus , syn .: Centaurea americana Nutt. ) Is a species of the genus Plectocephalus in the sunflower family (Asteraceae).
features
The American knapweed is an annual plant that reaches heights of 30 to 200 centimeters. The upright stem is simple or not very branched. The alternate and sessile or winged-stalked leaves are, glabrous or rough, dotted with glands, narrowly ovate to lanceolate and 8 to 20 centimeters long. The upper leaves have entire margins, the lower ones serrated.
The broad hemispherical flower head cover has a diameter of 3 to 5 centimeters. The bract appendages are straw-colored, not protruding and comb-shaped pinnate with about 15 sections. The cup-shaped inflorescence has a diameter of usually 4 to 8 (3 to 10) centimeters. The tubular flowers are pink or purple, rarely white. At the edge the tubular florets are asexual, sterile, zygomorphic and somewhat enlarged, 35 to 50 mm long. The inner tubular flowers are hermaphroditic, fertile , radially symmetrical , mostly lighter and 20 to 25 mm long.
The flowering period in Central Europe extends from July to August, otherwise from February.
The gray-brown to black achenes are 4 to 5 mm in size, hairless or with white hairs near their base. The pappus consists of stiff, uneven bristles 6 to 14 mm long.
The number of chromosomes is 2n = 26.
Occurrence
The American knapweed occurs in warm central North America from northeastern Mexico (Chihuahua, Coahuila, Nuevo León, San Luis Potosí, Tamaulipas) to the following states of the USA: Arizona, Arizona, Oklahoma, Texas, Missouri and Louisiana. It thrives in prairies , grasslands, fields, open forests and in disturbed locations at altitudes from 0 to 2100 meters. This species tends to grow wild ( invasive plant ).
use
The American knapweed is rarely used as an ornamental plant for summer borders and as a cut flower. It has been in culture since 1824 at the latest. There are some varieties whose flowers are dark purple or white.
literature
- David J. Keil: Plectocephalus in the Flora of North America , Volume 19, Page 176: Plectocephalus americanus - Online. (engl.)
- Eckehart J. Jäger, Friedrich Ebel, Peter Hanelt, Gerd K. Müller (eds.): Rothmaler excursion flora from Germany. Volume 5: Herbaceous ornamental and useful plants. Spectrum Academic Publishing House, Berlin Heidelberg 2008, ISBN 978-3-8274-0918-8 .
