common sowthistle

not listed

NNA - Not applicable

SNA - Not applicable

not listed

UPL - Obligate upland

FACU - Facultative upland

FACU - Facultative upland

Common sowthistle is a 4″ to 80″ tall, erect, annual forb that rises on one or more stems from a short taproot.

The stems are erect, hollow between the nodes, hairless at least below the inflorescence, and usually somewhat covered with a whitish, waxy bloom (glaucous). They occasionally branch near the top. The base of the stem may be soft or hard but is never woody. When broken the stems exude a milky sap.

Middle stem leaves are alternate, soft, spatula-shaped, oblong to inversely egg-shaped, or lance-shaped, 2⅜″ to 13¾″ long, and ⅜″ to 6″ wide. They are deeply, irregularly lobed (pinnatifid). 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 triangular to lance-shaped and usually sharply pointed, sometimes rounded. The upper surface of the leaf blade is hairless and dull, not shiny. The lower surface is hairless and usually glaucous. 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 cluster of several flower heads at the end of the stem. The stalks of the inflorescence are sometimes hairless, usually sparsely covered with reddish-brown, spreading, glandular hairs. They sometimes have minute, cobwebby or wooly hairs toward the tip (just under the flower head).

The flower heads are ⅝″ to 1″ in diameter when fully open. The whorl of bracts at the base of the flower head (involucre) is ⅜″ to ½″ long and either contracted at the tip (bell-shaped) or not contracted at the tip (pitcher-shaped). The bracts of the involucre usually have a few reddish-brown, spreading, glandular hairs, and sometimes have minute, cobwebby or wooly hairs toward the base. Each flower head has 80 to 250 yellow ray florets and no disk florets. The ray florets are 5 ⁄16″ to ⅝″ long and have 5 small teeth at the tip. The flat, spreading, strap-like portion at the end of the ray floret is about the same length as the tube portion at the base.

The fruit is a ⅛″ long achene with 3 or 5 faint or prominent ribs on each face and a wrinkled surface. There is a tuft of microscopically barbed hairs at the tip.

4″ to 80″

Yellow

Perennial sow thistle (Sonchus arvensis) stem is always hard and sometimes woody at the base. The leaf auricles may be rounded or pointed. The flower heads are larger, 1″ to 1¾″ in diameter. The involucre is longer, 9 ⁄16″ to ⅞″ long. The ray florets are longer, ⅜″ to 1″ long. The achene is prominently 5 to 8 ribbed.

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

Prickly sow thistle (Sonchus asper) stem is always soft at the base. 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 achene is prominently 3 ribbed and is not wrinkled.

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

Moist to slightly dry. Fields, pastures, roadsides, disturbed places. Full or partial sun.

July to October

Sources

2, 3, 4, 5, 7, 22, 28, 29, 30.

Native to Northern Africa, Asia, and Europe. Introduced and naturalized in North America.

Plant

Flower Head

Leaves