Plectocephalus
Plectocephalus americanus
The Plectocephalus form a small genus of flowering plants in the subfamily Carduoideae within the sunflower family ( Asteraceae). The botanical genus name is derived from the Greek words plektos for woven and kephale for the head, and makes reference to braided fringes of the bracts.
Description
Plectocephalus species are annual herbaceous plant, reaching heights of growth from 30 to 200 inches depending on the type. Unlike many genera of the tribe Cynareae they are not thorny. The upright stems are branched. The alternate, basal and distributed along the stems arranged leaves are petiolate or sessile. The leaf margins are completely or perforated. The leaf surfaces are tomentose hairy and dotted tiny glandular.
The bloom conditions are individually or in open branched inflorescences. The inflorescence stems are Roehrig. The egg-shaped to hemispherical or bell-shaped basket shell has a diameter of 3 to 6 centimeters. In eight to ten rows are arranged like roof tiles, the uneven, narrow bracts. They have an entire edge and tips with the eponymous fringed appendages. The basket bottom is flat. The chaff leaves are bristly. The flower heads contain many flowers. As with the other Carduoideae only tubular flowers are also here, as opposed to the other sub- families exist. The rand union tubular flowers are ungeschlechtig, sterile, more or less zygomorphic and enlarged, they are pink to purple. The inner tubular flowers are fertile and radial symmetry or zygomorphic with very slender and long Kronröhren; they are pink or purple, cream to light yellow. The anthers are truant and have appendages.
The inverted egg-shaped or barrel-shaped achenes are more or less compressed and own a small Elaiosom on one side. The early sloping pappus consists of one to three rows of short bristles gebärtet tiny.
Systematics and distribution
The genus belongs to the subtribe Plectocephalus Centaureinae from the tribe Cynareae in the subfamily Carduoideae within the sunflower family ( Asteraceae). Plectocephalus is part of a basal group in the Centaureinae and is not closely related to Centaurea in the narrow sense.
The species from the New World of the section Centaurea L. sect. Plectocephalus ( D.Don ) DC. were separated from the genus Centaurea L. and forms the genus reactivated Plectocephalus D.Don. The generic name was already Plectocephalus 1830 by David Don in Robert Sweet: The British Flower Garden, Series 2, 1, plate 51 published. DC. presented these types then as a section in the genus Centaurea. The genus contains only Plectocephalus originally from North to South America native species.
The spread in Europe, the Mediterranean and the Near East species remain in the genus Centaurea. In Plectocephalus only one chromosome set of x = 13 occurs, whereas in Centaurea of x = 8, 9, 10, 11, 12, 13 or 15 Morphologically, the Plectocephalus differ only slightly from the derived and multiform Centaurea.
Based in the USA and Mexico At least two species are used as ornamental plants and have run wild in some areas.
The genus Plectocephalus include two to four types:
- American knapweed ( Plectocephalus americanus ( Nuttall ) D.Don, Syn: Centaurea americana Nuttall ): The home is in the U.S. states: Arizona, Arkansas, Kansas, Louisiana, Missouri, Oklahoma and Texas and in Mexico the states: Chihuahua, Coahuila, Nuevo Leon, San Luis Potosi and Tamaulipas. A variety is called ' Jolly Joker '.
- Plectocephalus chilensis G.Don ex Loudon: native Chile.
- Roth Rocks knapweed ( Plectocephalus rothrockii ( Greenman ) DJNHind, Syn: Centaurea rothrockii Greenman ): The home is in the U.S. states: Arizona, New Mexico and Mexico in the states: Chihuahua, Durango, Sinaloa and Sonora.
Swell
- David J. Keil: Plectocephalus. In: Flora of North America Editorial Committee ( eds.): Flora of North America North of Mexico. Volume 19: Magnoliophyta: unranked, part 6: Asteraceae, part 1 ( Mutisieae - Anthemideae ), Oxford University Press, New York / Oxford et al 2006, ISBN 0-19-530563-9, p 175 (English )