Sonchus asper (L.) Hill - Spiny-leaved Sow Thistle

Sonchus asper plant

Family - Asteraceae

Stems - To +1m tall ,erect, herbaceous, from taproot, fistulose, purplish, glabrous, glaucous, with milky sap, single or multiple from base, branching, often carinate.

Sonchus asper stemStem with aphids.

Leaves - Alternate, sessile, clasping, auriculate, with undulate spiny margins, deep shiny green above, glaucous below. Lowest leaves obovate to spatulate or somewhat lyrate-pinnatifid, to +15cm long. Upper leaves reduced, becoming ovate-lanceolate. Auricles spiny but round at the apex.

Sonchus asper leaf baseLeaf bases.

Inflorescence - Terminal loose corymbiform cluster. Cluster subtended by foliaceous bracts. Peduncles long, glaucous, occasionally with sparse glandular pubescence but typically glabrous. Small scarious bracts usually present at the divisions of the inflorescence or somewhere on the peduncles.

Sonchus asper inflorescenceInflorescence.

Involucre - To 1.5cm tall(long), +/-1cm in diameter at base, vase-shaped. Phyllaries imbricate. Outer phyllaries with small prickles at apex, shorter than inner phyllaries. Inner phyllaries in 3 or 4 series, to 1.5cm long, glabrous, innermost with scarious margins or completely scarious, linear.

Sonchus asper involucreInvolucre.

Ray flowers - Perfect, fertile. Flower heads to 2.7cm broad. Ligules to 6mm long, 1.5mm broad, 4-notched at apex, yellow. Corolla tube pubescent, 1cm long, white. Style bifurcate, pubescent. Achenes slightly flattened, ovoid to narrowly so, to 3mm long, 1.1mm broad, with 3 nerves on each side(6 total), glabrous. Pappus of numerous capillary bristles to 9mm long, white. Receptacle slightly concave in flower.

Sonchus asper flowers

Disk flowers - Absent.

Flowering - May - October.

Habitat - Waste ground, disturbed sites, roadsides, railroads.

Origin - Native to Europe.

Other info. - Because of the long pappus of the fruits, this plant can spread easily and quickly, and spread it has! This introduced weed can be found over much of the U.S. and continues to spread. The prickly leaves and big taproot make the plant difficult at best to remove from the ground. The milky sap is very sticky. A closely related species, S. oleraceus L. is also common and looks quite similar. The difference in the two plants lies in that S. oleraceus has leaf auricles which come to an acute point, those of S. aspera are always rounded. The lower leaves of S. oleraceus are nearly always deeply lyrate-pinnatifid. S. oleraceus is a much less stout species also which can be handled easily without injury to the person doing the handling.

Photographs taken at the Kansas City Zoo, 6-11-00, somewhere in North Carolina, 4-20-03, and off Lee Rd 54, Lee County, AL., 10-12-04.


Back