Centaurea solstitialis

Yellow star-thistle causes chewing disease and death in horses, and injures animals and humans with its long, spiny bristles. On the other hand, it is also used for honey production in some states.
Photo Credit: © Brother Alfred Brousseau, 1995 Saint Mary's College of California, @ USDA-NRCS PLANTS Database.
Centaurea solstitialis
Common Name: yellow star-thistle
Other Common Names: yellow star thistle, yellow starthistle
Plant Functional Group: Forb
Class > Order > Family: Magnoliopsida > Asterales > Asteraceae
What does the species look like?

Yellow star-thistle is an erect, annual to sometimes biennial, herbaceous plant, growing 0.25 to 3 feet tall, or more. Its tiny, yellow flowers are tightly clustered into flowerheads with the outer flowers sterile, and the inner flowers having both male and female parts. The flowerheads appear as one flower at the ends of branches, and they are pollinated by insects.

Yellow star-thistle prefers full sunlight, growing in deep, but well-drained soils. It is found in open grasslands and rangelands, cultivated fields and pastures, woodlands, riparian areas, and travel corridors.
Where is the species found?
States & Provinces
AB, AZ, CA, CO, CT, FL, IA, ID, IL, IN, KS, KY, MA, MB, MD, MI, MN, MO, MT, NC, ND, NE, NH, NJ, NM, NV, NY, OH, OK, ON, OR, PA, RI, SC, SD, SK, TN, TX, UT, VA, WA, WI, WV, WY
Special Considerations for Observing

If drought seems to be the cause of leaf senescence for a plant, please make a comment about it for that observation.
Which phenophases should I observe?
Do you see...?
Leaves Initial growth
New growth of the plant is visible after a period of no growth (winter or drought), either from above-ground buds with green tips, or new green or white shoots breaking through the soil surface. Growth is considered "initial" on each bud or shoot until the first leaf has fully unfolded. For seedlings, "initial" growth includes the presence of the one or two small, round or elongated leaves (cotyledons) before the first true leaf has unfolded.
More...


Leaves
One or more live, fully unfolded leaves are visible on the plant. For seedlings, consider only true leaves and do not count the one or two small, round or elongated leaves (cotyledons) that are found on the stem almost immediately after the seedling germinates. Do not include fully dried or dead leaves.
More...


Flowers Flowers or flower buds
One or more fresh open or unopened flowers or flower buds are visible on the plant. Include flower buds or inflorescences that are swelling or expanding, but do not include those that are tightly closed and not actively growing (dormant). Also do not include wilted or dried flowers.
More...

How many flowers and flower buds are present? For species in which individual flowers are clustered in flower heads, spikes or catkins (inflorescences), simply estimate the number of flower heads, spikes or catkins and not the number of individual flowers.

  • Less than 3
  • 3 to 10
  • 11 to 100
  • 101 to 1,000
  • More than 1,000
Open flowers
One or more open, fresh flowers are visible on the plant. Flowers are considered "open" when the reproductive parts (male stamens or female pistils) are visible between or within unfolded or open flower parts (petals, floral tubes or sepals). Do not include wilted or dried flowers.
More...

What percentage of all fresh flowers (buds plus unopened plus open) on the plant are open? For species in which individual flowers are clustered in flower heads, spikes or catkins (inflorescences), estimate the percentage of all individual flowers that are open.

  • Less than 5%
  • 5-24%
  • 25-49%
  • 50-74%
  • 75-94%
  • 95% or more
Fruits Fruits
One or more fruits are visible on the plant. For Centaurea solstitialis, two types of fruit are produced, both very tiny and seed-like and crowded into a spent flower head. One type has a tuft of white bristles and the fruit changes from whitish-yellow or yellow-green to grayish or tan, and the other type is without bristles and the fruit changes from whitish-yellow or yellow-green to brown. Both types drop or are blown from the plant after the spent flower head reopens. Do not include empty flower heads that have already dropped all of their fruits.
More...

How many fruits are present?

  • Less than 3
  • 3 to 10
  • 11 to 100
  • 101 to 1,000
  • More than 1,000
Ripe fruits
One or more ripe fruits are visible on the plant. For Centaurea solstitialis, a fruit is considered ripe when it has turned grayish, tan or brown and readily drops or is blown from the reopened flower head when touched. Do not include empty flower heads that have already dropped all of their fruits.
More...

What percentage of all fruits (unripe plus ripe) on the plant are ripe?

  • Less than 5%
  • 5-24%
  • 25-49%
  • 50-74%
  • 75-94%
  • 95% or more
Recent fruit or seed drop
One or more mature fruits or seeds have dropped or been removed from the plant since your last visit. Do not include obviously immature fruits that have dropped before ripening, such as in a heavy rain or wind, or empty fruits that had long ago dropped all of their seeds but remained on the plant.
More...

How many mature fruits have dropped seeds or have completely dropped or been removed from the plant since your last visit?

  • Less than 3
  • 3 to 10
  • 11 to 100
  • 101 to 1,000
  • More than 1,000
What do these phenophases look like?

There is currently no photoguide available for this species. If you'd like help us create one, use the guidance document and species template provided here. Then send it via email to education@usanpn.org when it is complete.

USDA PLANTS profile for yellow star-thistle (USDA Symbol: CESO3 )