Spiny sowthistle (Sonchus asper) is a summer annual weed with a basal rosette and an upright flowering stem.The leaves are deeply notched and wavy. Lower leaves are petiolate while the upper leaves are sessile. Seedlings of the two species(Sonchus asper & Sonchus oleraceus) are practically indistinguishable, and may be difficult to tell apart even at spray stage without examining the root system. Th… Spiny sow thistle is an annual pest in many parts of Western Canada, and has developed Group 2 herbicide resistance in Alberta. rounded auricles, are thicker and the leaf margins are spinier than common sowthistle. Sonchus oleraceus has short taproot and deeply lobed leaves. Leaves are lanceolate to oblanceolate in shape, hairless and dark green in color with pale white to purple veins. Spiny sowthistle is primarily a weed of pastures, hay fields, landscapes and roadsides.  It is found throughout the United States. Young leaves form a basal rosette have a whitish coating. The leaves have very prickly margins that initially develop as a basal rosette and then occur alternately along the flowering stem, the bluish-green color of the leaves, and the yellow flowers with a ‘puff-ball’ seedhead are all characteristics that help in the identification of spiny sowthistle. Clemson University. Sonchus asper is an annual or biennial herb sometimes reaching a height of 200 cm. Spiny Sow Thistle (Sonchus asper): An annual that has bluish-green leaves and stems that emit a milky sap when cut. 21 September, 2017. It is found throughout the United States. The leaves are bluish-green, simple, lanceolate, with wavy and sometimes lobed margins, covered in spines on both the margins and beneath. Biennial thistles spread only by seed (achenes) that are produced in great number by all the noxious species, ra… Annual and perennial sow thistle will be covered in an upcoming post. This is an annual weed, reproducing by seeds. All three sport spiky serrated leaves in a dense basal rosette in spring which rises up to a bushy mass midsummer, topped by stems 1 to 5 feet tall bearing … The species can overlap the winter and summer annual categories. Annual Sow Thistle Winter annual broadleaf plant. Spiny annual sow-thistle can be differentiated from annual sow-thistle by its dark green leaves with purplish margins. Mature Spiny Sow Thistle with Yellow Flowers, Chaparral (for bermudagrass pastures, will destroy bahiagrass), Cimarron Max (for bermudagrass pastures, will destroy bahiagrass), Pastora (for bermudagrass pastures, will destroy bahiagrass). Flower heads are numerous, yellow, and appear in corymbs. The root of spiny sowthistle is a taproot. Spiny sowthistle spreads by seed. Lower leaves are alternate, blue-green, 4 to 12 inches long with two to five lobes with prickly teeth on each side, gradually becoming smaller toward the top with a clasping base. Spiny sowthistle is a winter annual that is actually in the sunflower family and not a true thistle. The perennial sow thistle (Sonchus arvensis) is often confused with the annual sow thistle (Sonchus oleraceus). Lower leaf of perennial sowthistle. Spiny Sow-thistle (Sonchus asper) Common names: Spiny Sow-thistle: Sow Thistle: Prickly Sow Thistle: General Plant Information ; Plant Habit: Herb/Forb: Life cycle: Annual: Sun Requirements: Full Sun to Partial Shade: Water Preferences: Mesic: Flowers: Showy: Flower Color: Yellow: Bloom Size: Under 1" Flower Time: Summer Also, the leaf margins of spiny sowthistle are much more spiny or prickly than those of annual sowthistle. The stems are dark green in color (sometimes tinted with a reddish-purple tinge).