Cenchrus L.
Inner involucral spines flattened, connate for at least half their length
Burr 4–10 mm long, 3–6 mm diam., often purplish at the tips but pallid below, subtended by an outer ring of bristles. Annual herb with culms up to 90 cm long. Coast. Sands. Introd. from America. Fl. summer. Mossman River Grass Cenchrus echinatus
Burr 7–10 mm long, outer ring of bristles absent. Annual herb to 80 cm high. Sandy disturbed areas. Noxious weed. Introd. from America. Fl. summer–autumn Cenchrus incertus