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Barnaby's Thistle Centaurea solstitialis

Other Common Name(s):

Phonetic Spelling
sen-TAR-ee-uh sol-sti-shee-AL-liss
Description

Yellow Star Thistle is a winter annual in the Asteraceae family native to southern Europe and North Africa.  It grows on rangelands, pastures, agricultural areas, along highways or roads, railroad tracks, and other transportation or communication lines. It is dependent on seed production for growth and spread. A distinguishing characteristic is the bracts of the yellow flower heads contain stout, needle-like, straw-colored spines one to two inches long that radiate from the flower head in the shape of a star.  The bracts are light green, variably covered in cobwebby hairs and may become smooth. It is considered invasive in many of the western United States and upper mid-West. 

Yellow Star Thistle has a stout taproot and/or pubescent stems. Root growth during the winter and early spring is rapid and can extend well beyond 3 feet in depth. The stem is erect, slender, hairy and branching, and can grow up to three feet tall. 

Leaves are alternate and form a basal rosette of deeply lobed petiolate leaves covered in fine hair when young, up to 6 inches wide tapering to a short stalk.  This rosette will wither by the time the plant flowers.  All leaves are toothless and covered in woolly hairs giving a gray-green cast.  Leaves become much smaller, linear-oblong and undivided as they move further up the stem with the leaf bases extending down the stem, forming “wings." The wings are often wavy and may be broad with jagged or smooth edges.

Prefers well-drained soil of any type and any pH and can grow in nutritionally poor soil as well as very alkaline soils. It can tolerate drought.  It cannot grow in the shade. 

Genus came from the popular name of various plants in the late 14th century, from Medieval Latin centaurea, from Latin centaureum, from Greek kentaureion, from kentauros "centaur", so called because the plant's medicinal properties were discovered by Chiron the centaur.  Specific epithet means pertaining to the longest day of the year. This is in reference to the ability of Yellow Star Thistle to flower very late into the summer.

To control the plants, in small spaces before bolting, pull the plants by hand and dispose of them. Sheep, goats or cattle are effective in reducing Yellow Star Thistle seed production when grazed after plants have bolted but before spines form on the plant. Goats will eat Yellow Star Thistle even in the spiny stage.  When ingested by horses, it destroys the animal’s ability to chew and swallow and death occurs through starvation or dehydration.

Quick ID

  • Yellow thistle-like flowers
  • Long, sharp spines on the bracts in the shape of a star
  • Gray-green hairy foliage and winged stems 
See this plant in the following landscape:
Cultivars / Varieties:
Tags:
#invasive#weeds#yellow flowers#weedy#bracts#groundcover#self-seeding#acidic soils tolerant#wildflower garden#wavy leaves#problem for horses#non-toxic for dogs#non-toxic for cats#dry soils intolerant
 
Cultivars / Varieties:
Tags:
#invasive#weeds#yellow flowers#weedy#bracts#groundcover#self-seeding#acidic soils tolerant#wildflower garden#wavy leaves#problem for horses#non-toxic for dogs#non-toxic for cats#dry soils intolerant
  • Attributes:
    Genus:
    Centaurea
    Species:
    solstitialis
    Family:
    Asteraceae
    Life Cycle:
    Annual
    Recommended Propagation Strategy:
    Seed
    Country Or Region Of Origin:
    Southern Europe and North Africa
    Distribution:
    United States and the southern part of Canada
    Particularly Resistant To (Insects/Diseases/Other Problems):
    Dry soil and poor soil tolerant
  • Whole Plant Traits:
    Plant Type:
    Weed
    Wildflower
    Habit/Form:
    Dense
    Erect
    Growth Rate:
    Rapid
    Maintenance:
    High
    Texture:
    Medium
  • Cultural Conditions:
    Light:
    Full sun (6 or more hours of direct sunlight a day)
    Soil Texture:
    Clay
    Loam (Silt)
    Sand
    Shallow Rocky
    Soil pH:
    Acid (<6.0)
    Alkaline (>8.0)
    Neutral (6.0-8.0)
    Soil Drainage:
    Occasionally Dry
    USDA Plant Hardiness Zone:
    5b, 5a, 6a, 6b, 7a, 7b, 8a, 8b, 9a
  • Fruit:
    Fruit Color:
    Cream/Tan
    Display/Harvest Time:
    Fall
    Fruit Type:
    Achene
    Fruit Length:
    < 1 inch
    Fruit Width:
    < 1 inch
    Fruit Description:
    An achene (about a quarter-inch long) finely hairy, straw-colored at maturity with a tuft of short, stiff, light brown bristles at the tip; the seed often remains in the seed-heads until late fall or winter
  • Flowers:
    Flower Color:
    Gold/Yellow
    Flower Inflorescence:
    Cyme
    Head
    Flower Bloom Time:
    Fall
    Summer
    Flower Shape:
    Dome
    Flower Petals:
    7 - 20 petals/rays
    Flower Size:
    < 1 inch
    Flower Description:
    Yellow flowers have bracts armed with stout, needle-like, straw-colored spines one to two inches long that radiate from the flower head in the shape of a star
  • Leaves:
    Leaf Color:
    Gray/Silver
    Green
    Leaf Type:
    Compound (Pinnately , Bipinnately, Palmately)
    Leaf Arrangement:
    Alternate
    Rosulate
    Leaf Shape:
    Linear
    Oblong
    Leaf Margin:
    Lobed
    Undulate
    Hairs Present:
    Yes
    Leaf Length:
    3-6 inches
    Leaf Width:
    < 1 inch
    Leaf Description:
    Leaves are alternate and form a basal rosette up to 6 inches long when young, often lobed in narrow sections on the lower half of the leaf, and tapering to a short stalk. This rosette will wither by the time the plant flowers. All leaves are toothless and covered in woolly hairs giving a gray-green cast. Leaves become much smaller, linear-oblong and undivided as they move further up the stem with the leaf bases extending down the stem, forming “wings”. The wings are often wavy and may be broad with jagged or smooth edges.
  • Stem:
    Stem Color:
    Gray/Silver
    Green
    Stem Is Aromatic:
    No
    Stem Form:
    Straight
    Stem Surface:
    Hairy (pubescent)
    Stem Description:
    The stem is erect, slender, hairy and branching, and can grow up to three feet tall
  • Landscape:
    Landscape Location:
    Meadow
    Naturalized Area
    Problems:
    Problem for Horses
    Spines/Thorns
    Weedy