Annual sowthistle (Sonchus oleraceus)
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Annual sowthistle is a widespread winter or summer annual broadleaf plant. It is abundant in California to about 4900 feet (1500 m) and is commonly found in California's Central Valley and coastal areas where it grows year-round. Annual sowthistle inhabits agricultural land and other disturbed locations. It can harbor pests that are economically important to vegetable and fruit crops. Such pests include lettuce aphid, Nasanovia ribis-nigri, lettuce root aphid, Pemphigus busarius, green peach aphid, Myzus persicae, and nematodes. All are potential vectors of plant viruses.
Crop fields, orchards, vineyards, pastures, riparian areas, yards, gardens, roadsides, and disturbed sites.
Species are not easy to distinguish at the seedling stage. Cotyledons (seed leaves) are egg shaped to narrowly football shaped, hairless, short stalked and about 1/6 to 1/3 of an inch (4–8 mm) long. The first leaf is egg shaped, sparsely hairy, and the leaf edge is lined with backward pointing teeth. Leaves are alternate to one another along the stem.
Plants are coarse, erect, and can reach about 4-3/5 feet (1.4 m) in height. The stem is smooth, thick, hollow between stem joints (nodes), and secretes a milky sap when cut. The leaves are hairless somewhat bluish green. The upper leaves are smaller than the lower leaves, stalkless, and clasp the stems with clawlike basal lobes. Lower leaves are usually about 4 to 8 inches (10–20 cm) long, with a tapered or winged base, and are deeply lobed. The terminal leaf lobes are much larger than the lateral lobes.
Flowering generally takes place in the spring and summer and under favorable conditions, year-round. Flowers cluster at the stem tips to form daisylike flower heads. When closed the flower heads are urn shaped. Flower heads mature into white, fluffy seed heads, although not ball-shaped like in dandelions.
Fruits are football to egg shaped, flattened, and tiny—about 1/10 to 1/6 of an inch (2.5–4 mm) long. Attached to the fruit is a tuft of numerous, soft, fine, hairs.
Reproduces by seed.
Related or similar plants
- Blessed milkthistle, Silybum marianum
- Spiny sowthistle, Sonchus asper