Senecio triangularis
Senecio jacobaea
arrow-leaf groundsel, arrow-leaf ragwort, arrowleaf butterweed, groundsel
stinking willie, tansy ragwort
glabrous or sparsely floccose-tomentose when young.
sparsely and unevenly tomentose, glabrescent except in leaf axils and among heads.
single or loosely clustered.
(often purplish-tinged) usually single, sometimes loosely clustered.
evenly distributed; petiolate;
blades narrowly triangular, (3–)4–10+ × 2–6 cm, bases usually ± truncate, sometimes tapered, margins usually dentate, rarely subentire (distal leaves subsessile, smaller).
± 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).
± 8;
corolla laminae 9–15 mm.
± 13;
corolla laminae 8–12 mm.
(± 8) ± 13 (± 21), 6–10 mm, tips usually green, rarely black.
± 13, 3–4(–5) mm, tips black or greenish.
of 2–6 bractlets (rarely more than 2 mm).
of 2–6 (inconspicuous) bractlets (less than 2 mm).
10–30(–60) in corymbiform to subracemiform arrays.
(10–)20–60+ in corymbiform arrays.
glabrous.
all sparsely hairy or ray cypselae glabrous.
= 40, 80.
= 40.
Senecio triangularis
Senecio jacobaea
Plants of Senecio triangularis with narrow, subentire leaves that taper to the petioles are occasionally encountered in acid bogs in Oregon and Washington and less frequently elsewhere. They are regarded as edaphic variants; they have been recognized as var. angustifolius.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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.)
SW CO Wildflowers- 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
