Senecio serra Hook.

Varieties of Senecio serra are distinguished by head size and distribution.

Perennials, 40–100(–250) cm (caudices ligneous, branched). Herbage glabrous or lightly floccose-tomentose proximally when young. Stems single or loosely clustered. Leaves evenly distributed (proximal often withering before flowering); petiolate or subsessile; blades lanceolate or narrowly lanceolate to sublinear, 5–15(–20+) × (1–)1.5–4 cm, bases tapered, margins dentate to subentire (distal leaves smaller, bractlike). Heads 30–90+ in corymbiform to subpaniculiform arrays. Calyculi of 2–6 linear to filiform bractlets (0.5–5 mm). Phyllaries ± 8 or ca. 13, 4–9 mm, tips usually green, sometimes black. Ray florets ± 5 or ± 8; corolla laminae 5–10 mm. Cypselae glabrous or glabrate. 2n = 40.

Senecio serra is a species of flowering plant in the aster family known by the common names tall ragwort 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.

Senecio serra adalah spesies tumbuhan yang tergolong ke dalam famili Asteraceae. Spesies ini juga merupakan bagian dari ordo Asterales. Spesies Senecio serra sendiri merupakan bagian dari genus Senecio. Nama ilmiah dari spesies ini pertama kali diterbitkan oleh Hook..