Sonchus oleraceus (Annual Sow-Thistle) - photos and description




Leaves mid stem with a large terminal lobe.

Leaf upper stem not pinnate, ears at base of leaves are acutely pointed.

Leaf upper stem not pinnate, ears at base of leaves are acutely pointed.

 Leaf lower stem, ears at base of leaves are acutely pointed.

General: A weedy annual species with lobed leaves. Stem is hollow, and the stem's surface is angled. Plants mostly glabrous, involucre with glandular hairs. 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. Involucre bracts are overlapping. Flower heads measured to 17 mm in diameter. Flowers close by early afternoon.

Leaves: Leaves are alternate, clasping, more or less pinnate often with a large terminal lobe. Upper leaves somewhat prickly. Upper leaves reduced in size and less divided. Leaf mid stem was measured at 15 cm long including a terminal lobe that was 6.5 cm long.

Height: Height listed in Budd's Flora to 200 (!) cm tall, we measured plants to only 32 cm tall.

Habitat: Gardens, roadsides, disturbed soil.

Abundance: Fairly common.

Origin: Introduced.

Similar species: Very similar to Sonchus asper. 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 September 16th, in our garden in our home city of Regina, SK.