Sonchus asper (Prickly Sow-Thistle) - photos and description



Leaves have rounded auricles.

Lower stem leaf in above photo.

Basal leaf in above photo.

General: A weedy annual species with prickly leaves. Stem is hollow, and the stem's surface is angled. Plants mostly glabrous. When these plants are bruised they exude a milky sap.

Has been declared a noxious weed in Saskatchewan.

Flowers: Flower heads ligulate, bright yellow in colour, grow in a terminal panicle. Flower heads measured to 17 mm in diameter. Flowers close by late morning.

Leaves: Leaves are alternate, spatulate, upper leaves clasping with rounded auricles. Upper leaves very prickly. Leaves reduced upwards. Upper leaf highlighted in photo above was 14 cm long by 4 cm wide. Lower and basal leaves have long petioles. Basal leaf highlighted in photo above was 16.5 cm long by 3.5 cm wide.

Height: Height listed in Budd's Flora to 150 cm tall, we measured plants to only 30 cm tall.

Habitat: Gardens, roadsides, disturbed soil.

Abundance: Common.

Origin: Introduced.

Similar species: Very similar to Sonchus oleraceus. To distinguish the species examine the leaf auricles (the ears at the base of the leaves). Sonchus asper has leaf auricles that are rounded and not at all acute; whereas Sonchus oleraceus has leaf auricles with a distinctly acute base.

In the few plants of each species we've observed, Sonchus asper was much more prickly than Sonchus oleraceus.

When and where photographed: Photos taken August 8th, bare soil in shrub bed along walking path, in our home city of Regina, SK.