spotted knapweed
Centaurea stoebe ssp. micranthos (Gugler) Hayek
Description from Invasive.org
Appearance
Centaurea stoebe ssp. micranthos is an herbaceous biennial or perennial plant that readily invades open areas. Its name is derived from the black margins of the flower bract tips which give the flower heads a spotted look.
Foliage
A basal rosette of deeply lobed leaves is produced the first year. Rosette leaves are deeply lobed, petiolate, and approximately 8 in. (20 cm) long. Flowering stems are 1-4 ft. (0.3-1.2 m) tall and branched. Stem leaves are alternate and may be slightly lobed or linear. Leaves become smaller and less lobed toward the apex.
Flowers
The small purple to pink flowers bloom in the early summer.
Fruit
Reproduction of spotted knapweed occurs solely by seed. Hundreds and/or thousands of seeds are produced. Seeds are easily distributed by wind, animals, and contaminated hay. Seeds can remain viable in the soil for up to 8 years.
Ecological Threat
Centaurea stoebe ssp. micranthos invades a wide variety of habitats including pastures, open forests, prairies, meadows, old fields, and disturbed areas. It displaces native vegetation and reduces the forage potential for wildlife and livestock. It is native to Europe and western Asia. It was accidentally introduced into North America in contaminated alfalfa and clover seed in the late 1800s.
Resources
- Program Aid - USDA APHIS PPQ
- Biology and Biological Control of Knapweed - USDA Forest Service
- Biological Control of Invasive Plants in the Eastern United States - USDA Forest Service
- Weeds Gone Wild: Alien Plant Invaders of Natural Areas - Plant Conservation Alliance
- Element Stewardship Abstract - The Nature Conservancy
- Fire Effects Information System - USDA Forest Service
- Know Your Knapweeds - North Dakota State University
- Weed of the Week - USDA Forest Service
- Weed Field Guide - USDA Forest Service
- Plant Invaders of Mid-Atlantic Natural Areas - National Park Service and U.S. Fish and Wildlife Service
Selected Images from Invasive.org
View All Images at Invasive.org
Joseph M. DiTomaso, University of California - Davis, Bugwood.org
Additional Resolutions & Image Usage
Norman E. Rees, USDA Agricultural Research Service - Retired, Bugwood.org
Additional Resolutions & Image Usage
John M. Randall, The Nature Conservancy, Bugwood.org
Additional Resolutions & Image Usage
Steve Dewey, Utah State University, Bugwood.org
Additional Resolutions & Image Usage
Ken Chamberlain, The Ohio State University, Bugwood.org
Additional Resolutions & Image Usage
John M. Randall, The Nature Conservancy, Bugwood.org
Additional Resolutions & Image Usage
Joseph M. DiTomaso, University of California - Davis, Bugwood.org
Additional Resolutions & Image Usage