Perennial Sowthistle (Sonchus arvensis)

Family:

Sunflower Family (Asteraceae)

Other Names:

corn sow thistle, creeping sow thistle, dindle, field milk thistle, field sow thistle, gutweed, hare's colewort, hare's lettuce, hare's palace, milk thistle, swine thistle, swinies, tree sow thistle.

Origin and Distribution:

Perennial sowthistle originated in Europe and western Asia. After immigrating to North America, presumably as a contaminant of crop seed, the species spread throughout southern Canada and northern U.S. but remained scarce in most southern and central states. In Ohio, the plant occurs frequently in the northeast and is sparsely distributed elsewhere. Perennial sowthistle inhabits disturbed areas such as pastures, roadsides, waste places, lakeshores, gardens, lawns, and no-tillage agronomic fields. The plant is adapted to many soil types but grows most abundantly on rich loams. It prefers moist rather than dry conditions.

Plant Description:

Perennial sowthistle can be difficult to distinguish from several other closely-related weeds based on above-ground growth. Most of the species have hollow stems, lobed leaves with irregular teeth ending in weak prickles, and yellow flowers that appear similar to dandelion flowers but smaller. Also, all of these plants exude a sticky white juice when cut or bruised. Roots of perennial sowthistle are unique, however, in that they spread horizontally and are much more extensive than the simple taproot formed by other similar species. Perennial sowthistle reproduces by seeds and large colonies can become established from stems arising from buds on creeping roots.

  • Root System:

    The root system is extensive and composed of downward- and horizontally-growing roots, which are fleshy, brittle, cord-like, and have buds that give rise to new stems

  • Seedlings and Shoots:

    Seedlings have club-shaped leaves with irregularly-toothed edges and a dull bloom on the lower surface. Leaves of shoots arising from roots are deeply-lobed and have wavy edges with irregular, spiny teeth. Leaf stalks (petioles) are winged with bases that encircle the stem. All leaves including the first two seed leaves (cotyledons) contain milky juice

  • Stems:

    Stems are smooth, hollow, stout, ridged, over 4 feet tall, and contain milky juice. Stems are hairless on the lower part but upper parts, branches, and flower stalks may have hairs that appear dark due to tiny glands located at the tip.

  • Leaves:

    Leaves are alternate (1 leaf per node), 4 to 8 inches long, dull, blue-green, and crowded on the lower half of the stem. On either side of the midrib are 2 to 5 (rarely 7) deep lobes. Leaf edges are irregularly-toothed and each tooth ends with a weak prickle. Lower leaves attach to the stem by way of winged petioles. Leaves located in the middle and upper portions of the stem have shorter petioles and lobed bases that encircle the stem. Uppermost leaves are small, often unlobed, and usually scarce. Contained in leaves is a milky juice.

  • Flowers:

    Flower heads are 1 1/2 inches wide and composed of many yellow ray flowers. Flowers have an appearance similar to that of dandelion flowers but smaller and, instead of being solitary, many flower heads are clustered at the ends of branched stems.

  • Fruits and Seeds:

    Single-seeded fruits are about 1/8 inch long, brown, oval, with 5 to 7 longitudinal wrinkled ribs. At the top is a soft white tuft of hair (pappus).

Similar Species:

Perennial sowthistle has an extensive root system distinguishing it from annual sowthistles (Sonchus species) that produce only taproots. Prickly lettuce (Lactuca canadensis) leaves are also lobed with prickly edges but the midribs have a row of stiff sharp prickles on the underside.

Biology:

There is currently disagreement over how to delineate this species; some perennial sowthistles have glandular hairs while other do not and some authorities assign the hairless taxa to a separate variety named Sonchus arvensis var. glabrescens or a different species called Sonchus uliginosus. Perennial sowthistle flowers from June to October. A single plant can produce up to 9,750 seeds. New shoots arise from root segments 1 inch long or longer, so tillage can fragment and disperse roots thus enlarging the population by giving rise to new plants. Herbicides are available that, if applied in the late rosette to bud stage, provide good control. However, perennial sowthistle is relatively resistant to many common herbicides. The most effective system for control is a combination of cultural and chemical methods.

Toxicity:

None known.

Facts and Folklore:

  • 'Sonchus', the name given sow thistle by the Romans, is Latin for ''hollow'' referring to the plant's hollow stems.

  • 'Arvensis' refers to the plants affinity for cultivated areas.

  • Perennial sowthistle is said to be a favorite of rabbits, hence the many common folk names referring to hares. It was believed predators can not disturb a rabbit sitting beneath the plant.