Senecio jacobaea
Senecio serra
stinking willie, tansy ragwort
butterweed groundsel, sawtooth groundsel, serrated ragwort, tall butterweed, tall ragwort
sparsely and unevenly tomentose, glabrescent except in leaf axils and among heads.
glabrous or lightly floccose-tomentose proximally when young.
(often purplish-tinged) usually single, sometimes loosely clustered.
single or loosely clustered.
± evenly distributed (basal often withering before flowering); petiolate (sometimes obscurely);
blades ovate to broadly ovate (usually 1–3-pinnate, lobes mostly obovate to spatulate), (4–)7–20(–30) × (1–)2–5(–12) cm, bases usually tapered, ultimate margins dentate (distal leaves similar, smaller).
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).
± 13;
corolla laminae 8–12 mm.
± 5 or ± 8;
corolla laminae 5–10 mm.
± 13, 3–4(–5) mm, tips black or greenish.
± 8 or ca. 13, 4–9 mm, tips usually green, sometimes black.
of 2–6 (inconspicuous) bractlets (less than 2 mm).
of 2–6 linear to filiform bractlets (0.5–5 mm).
(10–)20–60+ in corymbiform arrays.
30–90+ in corymbiform to subpaniculiform arrays.
all sparsely hairy or ray cypselae glabrous.
glabrous or glabrate.
= 40.
= 40.
Senecio jacobaea
Senecio serra
Senecio jacobaea is a weed introduced from Europe and now well established in places of cool, damp summers. It is toxic to livestock and legally noxious in most states and provinces where it occurs.
The Russian botanist E. Wiebe (2000) resuscitated Jacobaea for plants that are treated here as Senecio jacobaea, S. erucifolius, and S. cannabifolius. Phylogenetic studies may confirm the utility of recognizing Jacobaea as a distinct genus; to do so here would be premature.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Varieties 2 (2 in the flora).
Varieties of Senecio serra are distinguished by head size and distribution.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Heads 40–90+; phyllaries ± 8, 4–6 mm; ray florets ± 5, corolla laminae 5–7 mm; disc florets 10–20 | var. serra |
1. Heads (12–)30–50; phyllaries ± 13, 7–9 mm; ray florets ± 8, corolla laminae 7–10 mm; disc florets 20–40+ | var. admirabilis |
- Local floras:
BC, 
CA, 
OR, 
WA - Local Web sites: CalFlora, CalPhotos,
Flora NW, 
Go Botany, 
IL Wildflowers, 
MI Flora, 
PNW Herbaria, Turner Photog. 
WildflowerSearch
iNaturalist (observations)
USDA Plants Database- LBJ Wildflower Center
- SEINet
- Plants of the World Online
- Encyclopedia of Life
- Wikipedia
- Google Image Search
