SafePlants

Spotted Knapweed

Spotted knapweed, a significant invasive plant, presents various considerations for homeowners, pet owners, and those concerned about ecological balance.

Considerations for Pets

• Spotted knapweed is described as poisonous to other plants (phytotoxic). While this doesn't directly translate to toxicity in animals, it is an indication of active chemical compounds.
• The plant has prickly stems.

Considerations for Children

• The plant has prickly stems.

Taxonomy and Nomenclature

• Scientific Name: Centaurea biebersteinii DC. (accepted name). Previously known as Centaurea maculosa and commonly referred to as Centaurea stoebe subsp. micranthos (Gugler) Hayek.
• Family: Asteraceae (Sunflower Family)
• Synonyms: Centaurea maculosa, Centaurea stoebe subsp. micranthos (Gugler) Hayek, Centaurea stoebe.
• Common Names: Spotted Knapweed (English), Gefleckte Flockenblume (German), Gewhnliche Rispen-Flockenblume (German).

Distribution and Habitat

• Native to Europe and western Asia, including central and southeast Europe, northern Italy, and eastern Oregon.
• Introduced to North America in the late 1800s.
• Now found in the northeast and north-central U.S., along the Pacific Coast, and throughout much of Idaho and Montana.
• Infests a variety of natural habitats, including barrens, fields, forests, prairies, meadows, pastures, and rangelands.
• Thrives in sunny sites and is especially troublesome in sandy, low-productivity sites, including grasslands.
• Can be found in dry pastures, valleys, and southeast-facing dry slopes.

Ecological Role

• Invasive exotic species that spreads quickly.
• Spreads rapidly in artificial corridors.
• Replaces native vegetation when it moves into an area.
• Highly competitive plant that easily and quickly crowds out native grass and plant species.
• Considered a serious threat to rangelands, especially in the western United States.
• Spotted knapweed ranks as the number one weed problem on rangeland in Montana.
• Spotted knapweed is poisonous to other plants (phytotoxic).

Morphological Characteristics

• Biennial or short-lived perennial herb.
• Grows 2 to 4 feet tall.
• Has pink flowers.
• Has prickly stems.
• Has a strong taproot as well as lateral roots.
• Blooms from July through August.
• Bolts (grows long stems from the basal rosette of leaves) in early May.
• Prolific seed producer, growing up to 900 seeds per plant annually.

Quirky Facts

• Spotted knapweed seeds can remain dormant for up to 8 years.
• The name "Knapweed" is derived from the Anglo-Saxon word "cnaep," meaning top, knob, or button, and refers to the flower bud.

Interactions with Other Organisms

• Spotted knapweed is poisonous to other plants (phytotoxic).
• Subject to biocontrol efforts, including studies on the seasonal dynamics of Urophora quadrifasciata.

Further Information

• Center for Invasive Species and Ecosystem Health
• Invasive Plants : http://www.na.fs.fed.us/fhp/invasive_plants.