Montane. Moist woodlands, openings, streamsides. Summer.
Roaring Fork Road, July 26, 2004.

Tall and in an open airy pattern, this Senecio likes subalpine woods and openings.  Notice the long, narrow, tapering, finely serrated (thus, "serra") leaves. Extensive patches are quite common.  See Senecio triangularis immediately below for a comparison with S. serra; the two plants are very similar.

David Douglas (of Douglas Fir fame) first collected this plant "common on the banks of the Wallawallah, Flathead, and Spokan Rivers" (as quoted in  Intermountain Flora). The plant was named by William Hooker in his Flora Boreali-Americana in 1834.

Montane. Moist woodlands, openings, streamsides. Summer.
Roaring Fork Road, July 26, 2004.

Montane. Moist woodlands, openings, streamsides. Summer.
Roaring Fork Road, July 26, 2004.

Montane, alpine. Moist woodlands, openings, streamsides. Summer.
Kilpacker Trail, July 22, 2004.

This and Senecio serra can be difficult to tell apart, for they both grow in moist or wet woods in large patches, are up to four feet tall, have narrow and serrated leaves, and are topped with many small, yellow sunflowers.  S. triangularis is, however, far more common than S. serra, enjoys much wetter areas, and is usually taller than S. Serra.  The strongest visually distinguishing characteristic is that the base of each Senecio triangularis leaf is broad and relatively perpendicular to the leaf axis, creating a triangular leaf shape.  The leaves of S. serra taper symmetrically from a narrow leaf base to a wider center and then back again to a narrow leaf tip.  Leaves of S. triangularis are shallowly saw-toothed; leaves of S. serra are finely serrated.  
S. triangularis often has more leaves, grows in more dense patches, and has slightly larger flowers with a more prominent central dome of disk flowers.

Thomas Drummond collected this plant, probably on his second trip to the United States in the early 1830s.  The plant was named by William Hooker, Drummond's mentor, in his Flora Boreali-Americana in 1834.

Montane, alpine. Woodlands, openings. Summer.
Sharkstooth Trail, July 31, 2004.

Montane, alpine. Woodlands, openings. Summer.
Kilpacker Trail, July 22, 2004.