Centaurea stoebe subsp. micranthos Hayek

Remark The words or terms in red (actually dark orange) in the text are defined in a glossary.


aug_22_01.gthmb can't be loaded. Centaurea stoebe subsp. micranthos is a biennial or short-lived perennial that blooms from midsummer to fall. The flowers are purple or rarely cream colored and the tips of the flower head bracts are black or dark brown, thus the common vernacular name Spotted knapweed. Centaurea stoebe subsp. micranthos was accidentally introduced to North America near the beginning of the twentieth century as a contaminant of alfalfa (Medicago sativa). It is one of the most pervasive weeds in western North America. In many places, it replaces native grasses and forbs often forming large-scale infestations, which have significant economic and aesthetic impacts to both agriculture and wildlands. Millions of acres of prime range and native habitat are infested throughout the northern Rocky Mountain states. Weeds of the Centaurea genus have more negative impacts to natural and agricultural ecosystems than any other. Centaurea stoebe subsp. micranthos will form dense stands on any open ground, excluding more desirable forage species and native plants.

The plant belongs to the Asteraceae family.

Name

In Greek κενταυριν (kentaurin) means Knapweed the standard common name of many Centaurea species. As for the name κενταυριν it is likely coming from κενταυροσ (kentauros) that means centaur. One of the famous centaur was Chiron, known for his exceptional goodness and wisdom and for his knowledge of medicinal plants. He raised Asclepius, a god of healing and taught him medicine which Asclepius went on to perfect. Since some species of Centaurea have been used as medicinal herbs, the genus name might come from the association of Chiron, centaur, to Centaurea. For an other origin of the name, some sources say that Chiron used the flower of some Centaurea species to heal wounds, including his own, after battle.

As for the first epithet of the name, stoebe, it is said to come from the Greek στοιβη ( stoibe) that means something used to stuff, to plug and was also the name of a thorny plant, identified as Poterium spinosum although Centaurea stoebe subsp. micranthos is in no ways thorny nor spiny...

As for the second epithet of the name, micranthos, that of the subspecies, it is from the Greek μικροσ (micros) that means small and ανθοσ (anthos) that means flower to specify that the flowers of Centaurea stoebe subsp. micranthos are smaller than those of the other subspecies.

Common names

The common vernacular name of Centaurea stoebe subsp. micranthos is Spotted Knapweed. Two French vernacular names are Centaurée maculée and Centaurée tachetée.

Synonyms

Centaurea stoebe subsp. micranthos has also been known as:

Identification

draw_2.jpg can't be loaded. Centaurea stoebe subsp. micranthos is somewhat similar to Centaurea diffusa and Centaurea repens and is is distinguished by its black-tipped involucral bracts. In North America, the name Centaurea maculosa has been misapplied to Centaurea stoebe subsp. micranthos; the later is polycarpic, tetraploid, originated in eastern Europe; the former is a biennial diploid from central Europe.

Description

In the first year of growth, Centaurea stoebe subsp. micranthos produces a rosette of deeply lobed basal leaves. In the following and subsequent years, each plant produces, one to ten multiply branched stems. The plants overwinter as a rosette and resumes growth in early spring. The seeds are capable of germinating in both early spring and fall. The plant usually grows in tufted clumps.

Roots

Stems

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Leaves

Flower heads

Fruits, seeds

Habitat

Centaurea stoebe subsp. micranthos is well adapted to a wide range of habitats including, but not limited to, open forests, urban interfaces, and rangelands. Although not well suited to riparian areas, it has been noted to invade streambanks and nearby meadows, wherever disturbance occurs or people visit. Though most common in disturbed sites, disturbance is not necessary for Centaurea stoebe subsp. micranthos to establish and thrive.

Distribution

map_na.jpg can't be loaded. In North America, Centaurea stoebe subsp. micranthos is abundant in British Columbia and the Northwestern United States. It is frequent in the Maritime Provinces of Canada, Ontario, and Québec. It is spreading into Saskatchewan and Alberta. The map shows the USA States and Canadian provinces where Centaurea stoebe subsp. micranthos can be found.

Notes

The leaves of Centaurea stoebe subsp. micranthos contain toxins, and allelopathic substances are exuded from roots. The allelopathic substances affect roots of other plants more than the stems and leaves.

Gallery

The photos of the gallery were taken either with one of the following: The title in the window shows the date when the picture was taken, i.e. jan_30_06... would mean that the photo was taken on the 30th of January, the 06 is for the 6th picture taken that day.

The month, day and picture number might be followed by a letter:

Click on the thumbnails to get larger view. The original photos are usually in TIFF format, the photos shown are generally in JPEG format, usually of dimensions one half (surface one quarter) for loading time reduction.

Plants

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Leaves

aug_22_02.mthmb cannot be loaded. The leaves on the right were scanned at 300 dpi, this allows to measure the dimensions of the leaves. aug_22_02s.mthmb cannot be loaded.

Flower heads

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