Sonchus arvensis ssp. arvensis

Native to Africa, Asia, and Europe. Introduced into the United States and naturalized.

Minnesota noxious weed

Minnesota prohibited weed seed

Urban areas, roadsides, streambanks. disturbed areas.

July to October

Yellow

16″ to 60″

This is a 16″ to 60″ tall, erect, perennial forb that rises on one or more stems from a deep, branched rhizome and creeping roots.

The stems are erect, hollow between the nodes, hairless at least below the inflorescence, and often somewhat covered with a whitish, waxy bloom (glaucous). They occasionally branch near the top. The base of the stem is hard, sometimes woody. When broken the stems exude a milky sap.

Middle stem leaves are alternate, oblong to lance-shaped, 2⅜″ to 15¾″ long, and ¾″ to 6″ wide. They are irregularly, deeply, pinnately lobed with 2 to 5 more or less triangular lobes per side. At the base of the leaf blade is a pair of ear-like projections (auricles) that wrap around no more than half of the stem. The auricles are small and usually rounded, sometimes pointed. The upper surface of the leaf blade is hairless and dull or only slightly shiny. The lower surface is hairless. The margins have sharp, spreading teeth with prickles at the tip. Basal and lower stem leaves are similar and are on winged leaf stalks. Upper leaves become gradually smaller, less lobed or unlobed, and have more prominent auricles.

The inflorescence is a small, sparingly branched array of up to 20 flower heads at the end of the stem. The stalks of the inflorescence are long and moderately to densely covered toward the tip (just under the flower head) with spreading, glandular hairs.

The flower heads are 1″ to 1¾″ in diameter when fully open. The whorl of bracts at the base of the flower head (involucre) is 9 ⁄16″ to ⅞″ long and either contracted at the tip (bell-shaped) or not contracted at the tip (pitcher-shaped). The bracts of the involucre have a central stripe of moderate to dense, spreading, gland-tipped hairs. Each flower head has 150 to 235 or more bright yellow to orangish-yellow ray florets and no disk florets. The ray florets are ⅜″ to 1″ long and have 5 small teeth at the tip. The flat, spreading, strap-like portion at the end of the ray floret is about as long as the tube portion at the base. The flowers are fragrant. They open 2 or 3 hours after sunrise and close around noon.

The fruit is a ⅛″ long achene with 5 to 8 prominent ribs on each face and a wrinkled surface. There is a tuft of microscopically barbed hairs at the tip.

Common sow thistle (Sonchus oleraceus) leaf auricles are triangular to lance-shaped and usually sharply pointed, rarely rounded. The lower surface of the leaf blade is pale and usually glaucous. The flower heads are smaller, ⅝″ to 1″ in diameter. The involucre is shorter, ⅜″ to ½″ long. The ray florets are shorter, 5 ⁄16″ to ⅝″ long. The achene is 3 to 5 ribbed.

Field sow thistle (Sonchus arvensis ssp. uliginosus) branches of the inflorescence are usually hairless, occasionally minutely hairy toward the tip (just under the flower head). The involucre is usually hairless, occasionally minutely hairy toward the base. The inflorescence branches and involucral bracts do not have gland-tipped hairs.

Hawkweed (Hieracium spp.) basal and lower stem leaves are not lobed.

Prickly lettuce (Lactuca serriola) leaves have a row of prickles along the midvein on the underside.

Prickly sow thistle (Sonchus asper) stem is soft at the base, not woody. The leaf auricles are always rounded, never pointed, and often wrap around more than half of the stem. The upper surface of the leaf blade is shiny. The lower surface is pale and usually glaucous. The flower heads are smaller, ⅝″ to 1″ in diameter. The involucre is shorter, ⅜″ to ½″ long. The ray florets are shorter, 5 ⁄16″ to ⅝″ long. The achene is prominently 3 ribbed and is not wrinkled.

Thistle (Cirsium spp., Carduus spp.) stems and leaves do not have milky sap.