sulphur knapweed
(Centaurea sulphurea)
This species is Introduced in the United States
ORIGIN: Mediterranean
GROWTH TRAITS: Upright, herbaceous winter annual typically growing 1-3’ tall (S-1 m) from a taproot. Large plants are branched; small plants have a single stem. Stems have wings ~¼” wide (5-6 mm) at their largest. Leaves are alternate, may be lightly toothed or lobed, and become smaller up the plant. Leaves and wings are yellow-green and sparsely covered with stiff hairs. Flowering occurs from May to July when 1” (2½ cm) flower heads develop singly at the ends of stems. Florets are yellow and numerous. Floral bracts are tipped with 3-5 pairs of small spines and a central main spine up to 1” long (2½ cm). Spines are straw-colored at their tips and dark brown at their bases. Seeds are ¼-S” long (5-8 mm), glossy, brownish-tan, and with dark brown pappus as long as seeds.
REPRODUCTION: By seed. It is unknown how long seeds remain viable in the soil, but seeds of related species are viable for up to three years.
HABITAT: Open, disturbed sites including grasslands, fields, pastures, roadsides, and waste places.
LOOK-ALIKES: The spiny capitula help differentiate this species from non-starthistle species in the Northwest. Yellow florets separate this species from purple-colored starthistles. Malta and yellow starthistle (Centaurea melitensis and C. solstitialis, both exotic) have yellow florets, but both have gray-green foliage due to numerous white cottony hairs. Flower heads of Centaurea sulphurea are larger than Malta and yellow starthistle, and Centaurea sulphurea seeds are twice as large and darker than seeds of the other two.
CITATIONS:
Winston, R.L., Andreas, J.E., Milan, J., DesCamp, W., Randell, C.B., and M. Schwarzlander. 2014. New Invaders of the Southwest. United States Department of Agriculture, Forest Health Technology Enterprise Team. FHTET-2014-12. Retrieved from https://bugwoodcloud.org/resource/files/14767.pdf
Winston, R.L., Andreas, J.E., Milan, J., DesCamp, W., Randell, C.B., and M. Schwarzländer. 2014. New Invaders of the Northwest. United States Department of Agriculture, Forest Health Technology Enterprise Team. FHTET-2014-12. Retrieved from https://www.fs.fed.us/foresthealth/technology/pdfs/FHTET-2014-12_NW_New_Invaders.pdf
GROWTH TRAITS: Upright, herbaceous winter annual typically growing 1-3’ tall (S-1 m) from a taproot. Large plants are branched; small plants have a single stem. Stems have wings ~¼” wide (5-6 mm) at their largest. Leaves are alternate, may be lightly toothed or lobed, and become smaller up the plant. Leaves and wings are yellow-green and sparsely covered with stiff hairs. Flowering occurs from May to July when 1” (2½ cm) flower heads develop singly at the ends of stems. Florets are yellow and numerous. Floral bracts are tipped with 3-5 pairs of small spines and a central main spine up to 1” long (2½ cm). Spines are straw-colored at their tips and dark brown at their bases. Seeds are ¼-S” long (5-8 mm), glossy, brownish-tan, and with dark brown pappus as long as seeds.
REPRODUCTION: By seed. It is unknown how long seeds remain viable in the soil, but seeds of related species are viable for up to three years.
HABITAT: Open, disturbed sites including grasslands, fields, pastures, roadsides, and waste places.
LOOK-ALIKES: The spiny capitula help differentiate this species from non-starthistle species in the Northwest. Yellow florets separate this species from purple-colored starthistles. Malta and yellow starthistle (Centaurea melitensis and C. solstitialis, both exotic) have yellow florets, but both have gray-green foliage due to numerous white cottony hairs. Flower heads of Centaurea sulphurea are larger than Malta and yellow starthistle, and Centaurea sulphurea seeds are twice as large and darker than seeds of the other two.
CITATIONS:
Winston, R.L., Andreas, J.E., Milan, J., DesCamp, W., Randell, C.B., and M. Schwarzlander. 2014. New Invaders of the Southwest. United States Department of Agriculture, Forest Health Technology Enterprise Team. FHTET-2014-12. Retrieved from https://bugwoodcloud.org/resource/files/14767.pdf
Winston, R.L., Andreas, J.E., Milan, J., DesCamp, W., Randell, C.B., and M. Schwarzländer. 2014. New Invaders of the Northwest. United States Department of Agriculture, Forest Health Technology Enterprise Team. FHTET-2014-12. Retrieved from https://www.fs.fed.us/foresthealth/technology/pdfs/FHTET-2014-12_NW_New_Invaders.pdf
Selected Images
Maps
EDDMapS Distribution - This map is incomplete and is based only on current site and county level reports made by experts, herbaria, and literature. For more information, visit www.eddmaps.org
State Lists - This map identifies those states that have this species on their invasive species list or law.
Invasive Listing Sources
Taxonomic Rank
| Domain: Eukarya |
| Kingdom: Plantae |
| Phylum: Magnoliophyta |
| Class: Magnoliopsida |
| Superorder: Asteranae |
| Order: Asterales |
| Family: Asteraceae |
| Subfamily: Carduoideae |
| Tribe: Cardueae |
| Genus: Centaurea |
| Centaurea sulphurea |
References
Common Name Reference: USDA, NRCS. 2010. The PLANTS Database. National Plant Data Center, Baton Rouge, LA, USA.
Scientific Name Reference: USDA, NRCS. 2010. The PLANTS Database. National Plant Data Center, Baton Rouge, LA, USA.