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Thickhead (Asteraceae) is a recently introduced summer annual that is very similar to the more common American burnweed. Seedlings form a rosette of elliptic leaves with toothed margins; midveins are often tinged red. Compared to American burnweed, seedling leaves are thicker and more deeply veined. As plants mature they grow upright to about 4 feet with toothed leaves clasping the stem. Thickhead flowers lack petals but are red in color. Additionally, thickhead flowers droop downward as though the plants were experiencing moisture stress. Seeds are wind dispersed and can produce multiple generations each growing season. Thickhead is controlled by most broad-spectrum nursery herbicides; however, herbicide efficacy rankings for this species are based on limited experimental data. [TOP]
