Centaurea stoebe subsp. micranthos Hayek
The words or terms in red
(actually dark orange) in the text are defined in a
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
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
In Greek κενταυριν
(kentaurin) means Knapweed the standard common name of many
As for the name
it is likely coming from
(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
( 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
that means small and
that means flower to specify that the flowers of
Centaurea stoebe subsp. micranthos are smaller than those
of the other subspecies.
The common vernacular name of
Centaurea stoebe subsp. micranthos is Spotted Knapweed.
Two French vernacular names are
Centaurée maculée and Centaurée tachetée.
Centaurea stoebe subsp. micranthos has also been known as:
- Acosta maculosa
- Centaurea biebersteinii DC.
- Centaurea maculosa Lam.
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.
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.
- Thick, deeply tap-rooted.
- Adding a ring of secondary xylem
- Between 1 to 3 feet long.
- Culminating in a single pinkish purple flower head.
- Of a distinctive gray-green color (as the leaves).
- The cauline leaves
- The upper leaves greatly reduced, mostly
undivided, linear to
- Of a distinctive gray-green color (as the stems).
- Very bitter to taste.
- About 3/4 inch in diameter.
- Without ray florets.
- The outermost disk florets
larger (15 to 25 mm), sterile, with 5
lobes, appearing at first glance to
but quickly proved otherwise.
- The innermost disk florets smaller (12 to 15 mm)
whitish to pinkish, fertile,
with pinkish-rose anthers.
- With an ovoid involucre.
- Phyllaries with prickle tips,
dark brown to black in upper half, green in lower half,
creating a spotted appearance that gives the plant its common name.
- Blooming from midsummer to fall.
- Achenes up to 3.5 mm long,
with a pappus of short
bristles up to 2 mm long.
- Whitish or pale brown.
- About a thousand seeds per plant.
- Extremely long-lived, able to remain viable in soil for eight
or more years.
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
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.
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.
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.
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.
- Minolta DiMAGE 7.
- Canon PowerShot A530
- Canon Xt Rebel, usually with the EF-S60mm f/2.8 Macro USM objective.
- EPSON Perfection 1650 (scanner).
The month, day and picture number might be followed by a letter:
- c for the Canon Xt Rebel.
- a for the Canon A530.
- m for the Minolta DiMAGE 7.
- s for the EPSON scanner.
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.
The leaves on the right were scanned at 300 dpi,
this allows to measure the dimensions of the leaves.