spotted knapweed
Family
AsteraceaeScientific Name
Centaurea stoebe ssp. micranthos
Other Common Names:
knapweed
Synonyms (former Scientific Names):
Centaurea biebersteinii
Acosta maculosa
Centaurea maculosa
Habit
An erect growing biennial or short lived perennialthat grows to 1.2 m, is freely branching with rough hair (like sandpaper) and has purple to pink to white flowers.
Leaves
Produce rosette leaves in the first year that are composed of compound leaves with several irregularly lobed segments. The leaves of the second season are alternate, 5-15 cm long, moderately hairy with translucent dots covering the leaf surface. If basal leaves are present they are long stalked.
Identifying Characteristics
Has floral bracts, like leaves directly below the flower, that are black tipped, with purple to pink (sometimes white) flowers, and leaves are covered with translucent dots. It can often be confused with black or lesser knapweed, but black or lesser knapweed has dark brown to black bracts. It can also be confused with meadow knapweed, which has dark brown to tan bracts, corn cockle and cornflower. However, the flowering leaves of spotted knapweed are more lobed. Stems are wirey and has hairs.
Flower Seed Head
Has purplish to pink flowers that are 6-10 mm wide and 8-12 mm long. Flower heads are oval in shape before they open and occur at the end of the stalks. Bracts around the flower appear brown with black tips often.
Seed Fruit
Each floret produces a single seeded achene. Seeds are around 2 to 3 mm long, oblong, and grayish brown in color. Seed surfaces will have 10 to 15 faint ridges and several white hairs about 0.2 mm long.
Where Found
Found in the northeastern United States and along the pacific coast and as far east as Virginia. It is not a serious problem in cultivated crops; however, its early spring growth allows it to become a problem in pastures. This plant also produces a chemical that prevents other plants from growing in close proximity to it. This very competitive plant settles itself in any disturbed soil robbing other plants of moisture and nutrients.
Growth Habit
upright and nonwoody
Thorns or Spines
not present
Approximate Flower Diameter
Varies:
pencil,
dime
Dominant Flower Color
Varies:
purple,
pink
Flower Symmetry
radial symmetery
Leaf Hairs
has hairs
Leaf Shape
Varies:
lance,
oval
Leaf Arrangement
Varies:
alternate,
rosette
Leaf Margin
lobed
Leaf Structure
Varies:
pinnate,
simple
Leaf Stalk
Varies:
none,
shorter than leaf
Stem Hairs
has hairs
Stem Cross Section
Varies:
round or oval,
square or multi-edged
Milky Sap
not present
Root Structure
taproot
Life Cycle
perennial
Ochrea
not present
Plant Type
Herb