Invasive Species: Centaurea solstitialis, Yellow Starthistle
Yellow starthistle invades a wide variety of habitats. It is an annual that can grow from 0.25 to 3 ft. (0.1 to 1 m) in height. Leaves near the base are petiolate, dissected, 2 to 6 in. (5 to 15 cm) long, and usually absent at time of flowering. Leaves further up the stem are decurrent, entire, and 0.4 to 4 in. (1 to 10 cm) long. Flowering occurs from June to October, when yellow flowers appear in heads at the tips of the branches. Bracts that subtend the flower head have small clusters of spines and stout central spines that are 0.4 to 1 in. (10 to 25 mm) in length. Yellow starthistle has two types of fruits or achenes. Most are cream to tan with a white pappus or plume; achenes in the outer ring are darker and lack a pappus. Yellow starthistle was accidentally introduced in the United States in the mid-1800s as contaminate of alfalfa seed. Yellow starthistle invades woodlands, pastures, roadsides, and fields. Yellow starthistle is poisonous to horses and can be fatal.
What are invasive species, and why should we be concerned about them?
Taxonomy: Scientific and Common Names for This Species
Asterales > Asteraceae > Centaurea solstitialis L.
Synonym(s): yellow star thistle, yellow star-thistle
Centaurea solstitialis – USDA PLANTS Profile
Distribution Maps
yellow starthistle – The reported distribution of this invasive species across the United States (Source: Invasive Plant Atlas of the United States)
Up-to-the-minute distribution maps and why they are important
Reporting This Invasive Species
What is the best way to report the occurrence of an invasive species?
How to report an invasive species sighting to EDDMapS – Early Detection & Distribution Mapping System
EDDMapS – Report an invasive species to EDDMapS.
County Extension Offices – Find your county Extension office on this map provided by USDA.
How to Identify
This invasive species can be identified by looking for the characteristics described in the paragraphs that follow.
Plant
Yellow starthistle is an annual that can grow from 0.25 to 3 ft. (0.1 to 1 m) in height.
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| Steve Dewey, Utah State University, bugwood.org | Steve Dewey, Utah State University, bugwood.org |
Foliage
Leaves near the base are petiolate, dissected, 2 to 6 in. (5 to 15 cm) long, and usually absent at time of flowering. Leaves further up the stem are decurrent, entire, and 0.4 to 4 in. (1 to 10 cm) long.
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| Mary Ellen (Mel) Harte, bugwood.org | Mary Ellen (Mel) Harte, bugwood.org |
Flower
Flowering occurs from June to October, when yellow flowers appear in heads at the tips of the branches. Bracts that subtend the flower head have small clusters of spines and stout central spines that are 0.4 to 1 in. (10 to 25 mm) in length.
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| Cindy Roche, bugwood.org | Mary Ellen (Mel) Harte, bugwood.org |
Fruit
Yellow starthistle has two types of fruits or achenes. Most are cream to tan with a white pappus or plume; achenes in the outer ring are darker and lack a pappus.
| bugwood.org | bugwood.org |
Native Centaurea Species Resemble Yellow Starthistle
Centaurea americana, American star-thistle – Images at invasive.org
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| Karan A. Rawlins, University of Georgia, bugwood.org | Karan A. Rawlins, University of Georgia, bugwood.org |
– Images at invasive.org
| bugwood.org | bugwood.org |
Additional Images for Yellow Starthistle
yellow starthistle – Images at invasive.org
Learning Resources for Yellow Starthistle
Additional Information, Biology, Control and Management Resources
Control and management recommendations vary according to individual circumstances. Location, habitat, weather, and a variety of other conditions are factors that help determine the best treatment choice. To find the safest and most effective treatment for your situation, consult your state’s land-grant institution. If you will use chemicals as part of the control process, always refer to the product label.
United States Land Grant University System – Find your Land Grant University’s College of Agriculture, University Cooperative Extension Service, or other related partner on this map provided by USDA.
Biology and Biological Control of Yellow Starthistle – USDA Forest Service
Weeds Gone Wild: Alien Plant Invaders of Natural Areas – Plant Conservation Alliance
Element Stewardship Abstract – The Nature Conservancy
Weed of the Week – USDA Forest Service
Centaurea solstitialis, Yellow Starthistle – Fire Effects Information System
Noxious Weed Management Program – Colorado Department of Agriculture
Invasives Database – TexasInvasives.org
Invasive Plants of California’s Wildland – California Invasive Plant Council
Global Invasive Species Database – Invasive Species Specialist Group