Senecio serra

{{Short description|Species of flowering plant}}

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|taxon = Senecio serra

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Senecio serra is a species of flowering plant in the aster family known by the common names tall ragwort{{PLANTS|id=SESE2|taxon=Senecio serra|access-date=10 November 2015}} and sawtooth groundsel. It is native to the western United States, where it can be found in several types of habitat, including sagebrush and woodlands. It is a perennial herb producing a single erect stem or a cluster of stems from a branched, woody caudex. The plant can exceed two meters in height. It is hairless in texture, with young plants sometimes appearing fuzzy, and green to red-tinged in color. The leaves have lance-shaped blades up to 20 centimeters long borne on short petioles, the leaves occurring evenly all along the stems. The inflorescence is a spreading array of many flower heads, each lined with green- or black-tipped phyllaries. The heads contain yellow disc florets and 5 to 8 yellow ray florets each under a centimeter long.