Acroptilon repens (L.) DC.
(=Centaurea repens L.; Centaurea picris Pall. ex Willd.)
Family Asteraceae, Tribe Cynareae
NOTE: This species is actionable only when found in field or vegetable seed for planting; tolerance applies.
Russian knapweed, creeping knapweed
Fruit an achene, obovate or broadly elliptic, sometimes slightly curved in lateral view, 2–4 mm long, 1.3–2.5 mm wide, 0.7–1.4 mm thick, base narrow, truncate, cross sectional outline +/– elliptic. Glabrous, smooth, with a slight sheen and numerous low longitudinal ridges. Ivory, occasionally green or yellow tinged, sometimes mottled. Scar basal or oblique, variable in shape and color, often brown, granular. Pappus deciduous. Style base variable, cream to light yellow to light brown, mostly cylindrical, +/– flanged, surrounded by whitish ring. Embryo spatulate, cotyledons broad; endosperm absent.
most temperate areas of the world
native to Afghanistan, Armenia, Azerbaijan, Iran, Iraq, Mongolia, Turkey, European Russia
semi-arid to subhumid temperate regions, fertile sandy soils and other soil types; a weed in pastures, orchards, cultivated fields, roadsides, ditch banks, waste places
Acroptilon repens is a perennial herb up to 1 m tall, with creeping rhizomes and an extensive and longlived network of roots. Reproduction is primarily vegetative. New shoots arise from buds on the roots, as well as on root fragments spread by cultivation. Using a combination of adventitious shoots and allelopathic chemicals, this species rapidly colonizes new areas, forming dense, single-species stands. It is toxic to horses and avoided by grazing animals because of its bitter taste. Acroptilon repens is one of ten species covered under the Federal Seed Act for which tolerance is applicable to its introduction (7 CFR 361.6(a)(2)).