Sow Thistle
Sonchus oleraceus
Photographed in Phoenix, Maricopa Co., Arizona. May 2, 2004
Sow Thistle is a very common weed growing in urban areas of the Sonoran Desert in Arizona. In Phoenix, for example, it grows from cracks in pavement, gardens, and vacant lots. Plants germinate from seed in early spring and are blooming by mid March. The plants are quite tolerant of heat and survive through part of the summer. The yellow inflorescence is open briefly for one day and only at dawn. A dandelion-like pappus at the top of each small seed allows them to be readily distributed by the wind. The leaf shape is very similar to the dandelion's as well, but Sow Thistle grows taller and branches freely whereas the dandelion has the leaves all basal and the flowering stalk is unbranched. True dandelions are rare in the hot southwest deserts.