Mid-Atlantic Invaders Tool

Description

Appearance

Centaurea jacea is a perennial plant that grows 1-4 ft. (0.3-1.2 m) tall. The stems are ridged and may have purple stripes.

Foliage

The basal leaves are oblanceolate to elliptic and 2-10 in. (5 -25 cm) long. Leaves become smaller as they ascend the stem. These smaller leaves are lanceolate and attach directly to the stem.

Flowers

The brown bracts of the inflorescence give this plant its common name. Flowering occurs from June to October, when rose to purple flowers appear in 1-1.25 in. (2.5-3.2 cm) wide, solitary heads at the tips of the branches.

Fruit

Centaurea jacea produces small light brown, plumeless seeds; about 12 per head.

Ecological Threat

Centaurea jacea is an aggressive invader preferring moister, cooler conditions than other knapweed species. It can tolerate partial shade. It can invade grasslands, open woods, meadows, pastures, woodland clearings, and cutover areas of forest crowding out native plants or forage. Centaurea jacea is native to Europe.

Uses

Landscape Ornamental Use (GRIN): No

All Uses (GRIN): Potential seed contaminant

Distribution Map (EDDMapS)

Wetland Indicator

Summary: brown knapweed (Centaurea jacea) is a Terrestrial/Wetland species.

Atlantic and Gulf Coastal Plain (AGCP):

Mid-Atlantic Coastal Plain regions

Eastern Mountains and Piedmont (EMP):

Mid-Atlantic Piedmont and Mountain regions

Northcentral and Northeast (NCNE):

Northern parts of PA and NJ (and beyond)

Legend (data from U.S. Army Corps of Engineers)

OBL (Obligate wetland): Almost always occurs in wetlands (estimated probability > 99%) under natural conditions

FACW (Facultative wetland): Usually occurs in wetlands (estimated probability 67% - 99%), but occasionally found in non-wetlands

FAC (Facultative): Equally likely to occur in wetlands (estimated probability 34% - 66%) or non-wetlands

FACU (Facultative upland): Usually occur in non-wetlands (estimated probability 67% - 99%), but occasionally found in wetlands (estimated probability 1% - 33%)

UPL (Obligate upland): Occur almost always (estimated probability > 99%) in non-wetlands under natural conditions

Taxonomic Rank

Resources

• Weed of the Week - USDA Forest Service