Prickly Sow Thistle
Sonchus asper
Photographed along Mesquite Wash, Maricopa Co., Arizona. Aug. 1, 2009.
ANNUAL: Herbaceous annual that may grow low or taller depending on
conditions. Most leaves are basal, with progressively smaller leaves higher on
the stems. When broken, stems exude milky sap.
RANGE: A cosmopolitan weed native to Eurasia and now found throughout
North America.
LEAVES: Margins of the leaves typically have sharp prickles at the tip
of each dentition. During vegetative growth from late winter the leaves grow as a rosette close to the ground.
FLOWERS: Small, yellow, dandelion-like flower heads composed entirely of
yellow strap-shaped florets. Can flower almost anytime of year when moisture
has been adequate for growth.
FRUIT: The achene seeds bear a
pappus of many fine capillary bristles at the top and do not have a
beak at the top.
ARMED: The prickles can be surprisingly sharp.