Senecio hydrophiloides Rydb.

Plants of Senecio hydrophiloides from toward the western end of the range tend to have the heads more or less congested and eradiate and stems loosely clustered; plants from toward the eastern edge tend to have heads loosely arrayed and radiate and stems single. The two forms have been recognized as weakly defined species (or varieties), the former as Senecio foetidus and the latter as S. hydrophiloides. They intergrade so completely that they are best treated as a single, variable taxon. The use of the epithet foetidus for the broadly conceived single species was based on a bibliographic misunderstanding; the correct epithet is hydrophiloides (T. M. Barkley 1978; A. Cronquist 1994).

In 1900, Thomas Howell gave the name Senecio oreganus to a collection from Lake Labish, near Salem, Oregon. The area has seen much disturbance and development since Howell’s time, and the plant appears to be extinct in the region. The collection is difficult to exclude from S. hydrophiloides, and the collection is here regarded as an odd outlier of S. hydrophiloides, which is known chiefly from east of the Cascade uplift. Howell’s collection and therefore the name S. oreganus also have been treated within S. sphaerocephalus (T. M. Barkley 1978; A. Cronquist 1955); that attribution appears to be in error. The "type" materials are now in the herbarium of Oregon State University in Corvallis.

Perennials (biennials?), 30–100(–140) cm (caudices erect, roots fleshy-fibrous). Herbage usually glabrous or glabrescent (young plants sparsely tomentose). Stems usually single, sometimes 2–4 clustered (sometimes reddish-tinged). Leaves progressively reduced distally; usually petiolate (petioles often winged); blades elliptic to broadly lanceolate, 5–15(–20) × 2–7 cm, bases broadly to narrowly tapered, margins dentate to denticulate (distal leaves sessile, bractlike). Heads (6–)15–30+ in congested or loose, corymbiform arrays. Calyculi of 2–5 bractlets (less than 2 mm). Phyllaries (± 8) ± 13 (± 21), 4–9 mm, tips (minutely to prominently) black. Ray florets 0 or (± 3 or 5) ± 8; corolla laminae 5–10 mm. Cypselae glabrous. 2n = 40.

Senecio foetidus Howell; S. foetidus var. hydrophiloides (Rydberg) T. M. Barkley ex Cronquist; S. oreganus Howell

Senecio hydrophiloides is a species of flowering plant in the aster family known by the common names tall groundsel and sweet marsh ragwort. It is native to western North America from British Columbia and Alberta to northern California to Utah, where it grows in wet meadows and similar habitat. It is a biennial or perennial herb producing a single erect stem or a cluster of a few stems which may exceed one meter in maximum height. The plants are green to red in color and usually without hairs, but new growth can be woolly. The leaves are lance-shaped to oval with toothed edges, the blades up to 25 centimeters long and borne on long winged petioles. The leaves are firm and sometimes a bit fleshy. The inflorescence is a loose or dense cluster of up to 30 or more flower heads lined with black-tipped phyllaries. They contain many yellowish disc florets at the center and often have some yellow ray florets, though these are sometimes absent. Senecio Hydrophiloides can cause Dermatitis.

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

Senecio hydrophiloides là một loài thực vật có hoa trong họ Cúc. Loài này được Rydb. miêu tả khoa học đầu tiên năm 1900.