Sonchus asper
prickly sow thistle
Europe, western Asia, and northern Africa
SunFull Sun – Part Shade
WaterMedium
Overview
Sonchus asper is an erect taprooted annual in the family Asteraceae reaching 12-48 inches (30-120 cm) tall and 6-18 inches (15-45 cm) wide. Stems are erect, hollow, branching in the upper half, carrying milky latex throughout. Leaves are alternate, dark green, glossy, with stiff sharp prickly marginal spines that are stiffer and more piercing than those of S. oleraceus. Leaves are shallowly to moderately lobed or merely toothed (less deeply lobed than S. oleraceus) and are characteristically curled or crinkled on the surfaces. Leaf bases clasp the stem with large rounded auricles that press tightly against the stem. Flower heads are yellow, 0.6-1 inch (15-25 mm) in diameter, composed entirely of ligulate florets, in loose terminal clusters. Involucral bracts are smooth (not glandular-hairy, unlike S. arvensis). Fruit is a flattened achene with 3 ribs on each face (versus smooth faces in S. oleraceus), topped with a white pappus. A single plant produces 5,000-20,000 seeds. The species occurs widely in gardens and cultivated fields across the Pacific Northwest and shares dominance of the annual-Sonchus niche with S. oleraceus.
Native Range
Sonchus asper is native to Europe, western Asia, and northern Africa, in gardens, cultivated fields, roadsides, and disturbed ground from sea level to approximately 8,000 feet (2,400 m). Naturalized across all 50 U.S. states and all Canadian provinces, where it is widely distributed as an annual garden weed in the Pacific Northwest.Suggested Uses
Used in the three-species Sonchus spp. identification exercise: S. asper (stiff spines, curled leaves, rounded auricles, ribbed achenes) versus S. oleraceus (soft spines, deeply lobed, pointed auricles, smooth achenes) versus S. arvensis (perennial rhizomatous, large heads, glandular peduncles). The achene surface comparison (ribbed versus smooth) requires a hand lens and is taught in fruit morphology.How to Identify
Appearance
Size & Dimensions
Height1' - 4'
Width/Spread6" - 1'6"
Bloom Information
Yellow ligulate flower heads 0.6-1 inch (15-25 mm) in diameter in loose terminal clusters, borne June through October continuously over 8-12 weeks. Self-pollinating and insect-pollinated. Seeds mature 2-3 weeks after flowering and disperse by wind via the pappus. Multiple generations are possible per year in the Pacific Northwest.
Detailed Descriptions
Flower Description
Yellow; all-ligulate heads 0.6-1 inch (15-25 mm) in loose terminal clusters; June-OctoberFoliage Description
Dark green and glossy; carrying stiff prickly marginal spines; leaves curled and clasping the stem with large rounded auricles; milky latex; deciduousGrowing Conditions
Sun Requirements
Requires 4-10 hours of direct sunlight daily
• Full Sun: 6+ hours of direct sunlight
• Partial Shade: 3-6 hours of direct sunlight
• Full Shade: Less than 3 hours of direct sunlight