Acroptilon repens

(Linnaeus) de Candolle in A. P. de Candolle and A. L. P. P. de Candolle
in A. P. de Candolle and A. L. P. P. de Candolle, Prodr. 6: 663. 1838.
IntroducedIllustrated
Basionym: Centaurea repens Linnaeus Sp. Pl. ed. 2, 2: 1293. 1763
Synonyms: Acroptilon picris (Pallas ex Willdenow) C. A. Meyer C. picris Pallas ex Willdenow
Treatment appears in FNA Volume 19. Treatment on page 172.

Creeping roots usually dark brown or black, with scaly adventitious buds. Stems ± cobwebby-tomentose. Leaves: basal and proximal cauline often deciduous by flowering, blades oblong, 4–15 cm; mid and distal linear to linear-lanceolate or oblong, 1–7 cm. Involucres 9–17 mm, loosely cobwebby. Phyllaries: apices of inner acute or acuminate, densely short-pilose. Corollas 11–14 mm, tubes 6.5–7.5 mm, throats 2–3.5 mm, lobes 3–3.5 mm. Cypselae ivory to grayish or brown, 2–4 mm; pappus bristles white, 6–11 mm. 2n = 26.


Phenology: Flowering late spring–summer (May–Sep).
Habitat: Fields, roadsides, riverbanks, ditch banks, clearcuts, cultivated ground
Elevation: 0–2300 m

Distribution

V19-188-distribution-map.gif

Introduced; Alta., B.C., Man., Ont., Sask., Ariz., Calif., Colo., Idaho, Iowa, Kans., Minn., Mont., Nebr., Nev., N.Mex., N.Dak., Okla., Oreg., S.Dak., Tex., Utah, Wash., Wyo., Mexico (Baja California), c Asia.

Discussion

Acroptilon repens has been reported also from Arkansas, Illinois, Indiana, Kentucky, Louisiana, Michigan, Missouri, New York, Ohio, Virginia, and Wisconsin; I have not seen specimens from those states.

Acroptilon repens is a serious weed pest, especially in the western United States. It is a strong competitor in infested areas, often forming dense colonies, and has allelopathic effects on other plants growing nearby. It is very difficult to control or eradicate once it becomes established. It reproduces vigorously from seed and spreads from adventitious buds borne on deep-seated runner roots. Root fragments readily regenerate as new individuals after cultivation. In addition, Russian knapweed is very poisonous to horses, causing neurological symptoms. Because of its bitter taste, it is usually avoided by grazing animals, and consequently it tends to spread when more palatable plants are consumed.

Selected References

None.

Lower Taxa

None.

... more about "Acroptilon repens"
David J. Keil +
(Linnaeus) de Candolle in A. P. de Candolle and A. L. P. P. de Candolle +
Centaurea repens +
Alta. +, B.C. +, Man. +, Ont. +, Sask. +, Ariz. +, Calif. +, Colo. +, Idaho +, Iowa +, Kans. +, Minn. +, Mont. +, Nebr. +, Nev. +, N.Mex. +, N.Dak. +, Okla. +, Oreg. +, S.Dak. +, Tex. +, Utah +, Wash. +, Wyo. +, Mexico (Baja California) +  and c Asia. +
0–2300 m +
Fields, roadsides, riverbanks, ditch banks, clearcuts, cultivated ground +
Flowering late spring–summer (May–Sep). +
in A. P. de Candolle and A. L. P. P. de Candolle, Prodr. +
Introduced +  and Illustrated +
Acroptilon picris +  and C. picris +
Acroptilon repens +
Acroptilon +
species +