Acroptilon repens

Species

Acroptilon repens (L.) DC.

Synonyms

(=Centaurea repens L.; Centaurea picris Pall. ex Willd.)

Family

Asteraceae

Tribe

Cynareae

NOTE

NOTE: This species is actionable only when found in field or vegetable seed for planting; tolerance applies.

Common names

Russian knapweed, creeping knapweed

Disseminule

fruit

Description

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.

Identification considerations

The basal or oblique (rather than lateral) scar may help to distinguish A. repens from other similar achenes in the genus Centaurea.

Distribution

most temperate areas of the world

native to Afghanistan, Armenia, Azerbaijan, Iran, Iraq, Mongolia, Turkey, European Russia

Habitat

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

General information

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)).