Centaurea sulphurea

Species category

Weed

Common name

sulphur knapweed

Diagnostic characters

Planting unit

AcheneAchene:
A dry, hard, one-chambered, one-seeded indehiscent fruit, as in buckwheat (Fagopyrum) or sunflower (Helianthus). The fruit wall is not united with the seed coat.

Shape

Conical

Size

  • Length: 4–5 mm
  • Width: 2.5–3 mm
  • Thickness: 2–2.5 mm

Color

Black with light mottling

Texture

Dull. The pappusPappus:
Modified calyx in Asteraceae, composed of hairs, bristles, awns, or scales. The pappus-like structure attached to milkweed seeds is termed a coma. 
crown, hilumHilum:
The scar on the seed coat at the place of its detachment from the seed stalk (funiculus).
area, and the longitudinal line on the lateral sides are white.

Other structures

Scar is lateral at base and hook shaped.

Identification notes

PappusPappus:
Modified calyx in Asteraceae, composed of hairs, bristles, awns, or scales. The pappus-like structure attached to milkweed seeds is termed a coma. 
is black and units are pointed.

Noxious weed seed categories

State Noxious Weed: Arizona, California

AOSA examination list

Not included

Nomenclature

Family

Asteraceae

Valid name

Centaurea sulphurea Willd.

 Centaurea sulphurea.  Pointed, hooked achenes with a black pappus.
Centaurea sulphurea. Pointed, hooked achenes with a black pappus.