Click to read about the Erigeron genus.

Montane, subalpine.  Meadows.  Summer.
Robertson Pasture Trail, Abajo Mountains, Utah, August 16, 2011.

Erigeron subtrinervis is almost indistinguishable from Erigeron speciosus, and, in fact, Welsh (A Utah Flora) considers the taxon to be just a variety of E. speciosus.  The Flora of North America and John Kartesz, the ultimate authority for plant names on this web site, consider them each at the species level. Weber (Colorado Flora) lists them as separate species but says, that E. subtrinervis "may simply be a race of" E. speciosus.

Keys to the morphological details of E. subtrinervis and E. speciosus are almost identically worded. The Flora of North America separates the two species on the basis of their hairiness:

Both species have hairs along the margins of the leaves but only E. subtrinervis has hairs on the surface of its leaves.

The phyllaries of S. speciosus are "usually glabrous, sometimes sparsely [hairy]"; the phyllaries of E. subtrinervis are "moderately to densely [hairy]".

The stems of S. speciosus are "glabrous or sparsely [hairy]; the stems of E. subtrinervis are "moderately to densely [hairy]".

After this species was named and described Erigeron glabellum by Asa Gray in 1863 from a specimen collected by Hall and Harbour in Colorado in 1862, it was renamed and described by Rydberg in 1894 . "Subtrinervis" means "weakly 3-nerved".

Erigeron subtrinervis (Three-nerved Fleabane, Three-nerved Daisy)
Asteraceae (Sunflower Family)

Montane, subalpine.  Meadows.  Summer.
Robertson Pasture Trail, Abajo Mountains, Utah, August 16, 2011.

Erigeron subtrinervis (Three-nerved Fleabane, Three-nerved Daisy)
Asteraceae (Sunflower Family)

Montane, subalpine.  Meadows.  Summer.
Robertson Pasture Trail, Abajo Mountains, Utah, August 16, 2011.

Both E. subtrinervis and E. speciosus have hairs along the leaf margins, but notice that the surface of E. subtrinervis leaves (at least those at mid and upper stem level) has hairs. Also notice the hairy stem. As noted above, these latter two characteristics help to separate E. subtrinervis from E. speciosus.