Centaurea stoebe ssp micranthos (S.G. Gmel. ex Gugler) Hayek

Spotted Knapweed

Centaurea stoebe ssp. micranthos plant

Family - Asteraceae

Stems - To 1.5m tall, erect to reclining with age, herbaceous, branching, multiple from base, from taproot, arachnoid pubescent above, slightly scabrous, striate.

Centaurea stoebe ssp. micranthos stem

Leaves - Main cauline leaves alternate, deeply pinnatifid, (many lobes divided again), to +/-12cm long, +/-7cm broad. Ultimate divisions mucronate, scabrous, entire, oblong. Leaves in upper portions of stem greatly reduced, mostly undivided, scabrous, typically arachnoid pubescent, mucronate, linear to oblong.

Centaurea stoebe ssp. micranthos leafMain cauline leaf.


Inflorescence - Single flower head terminating stem in a loose paniculiform arrangement of the upper 1/2 of stems.

Involucre - To 1.2cm tall(long), 7-8mm in diameter, ovoid to slightly urcreolate in shape. Phyllaries with prickle tips, imbricate, with some arachnoid pubescence, dark brown to black in upper half, green in lower half. Margins pectinate.

Centaurea stoebe ssp. micranthos involucreInvolucre.

Ray flowers - Absent.

Disk flowers - Outermost flowers enlarged, sterile, 5-lobed. Lobes to 8mm long. Innermost flowers 5-lobed, whitish to pinkish, fertile. Lobes to 4mm long. Anthers pinkish-rose, exserted, connate around style, 2-3mm long. Achenes to 3.5mm long, brown to blackish in fruit, ridged, glabrous to sparse pilose. Pappus of short bristles to 2mm long.

Centaurea stoebe ssp. micranthos flower

Flowering - June - August.

Habitat - Waste ground, rocky ground, roadsides, railroads.

Origin - Native to Europe.

Other info. - This plant is considered a pest almost every place it grows outside of cultivation. It is most common in the southern and especially the southwestern portions of Missouri.
At first glance the large sterile disk flowers appear to be ligules, but a quick second look will prove otherwise. The plant grows tall and gets very thin and open, much like in the large picture above.

Photographs taken at Logan Creek, Reynolds County, MO., 6-20-03.