Plant Species of the Bright Angel Trail: hoary-aster, Machaeranthera canescens

See Plant Guide to Bright Angel Trail for an introduction to this page.


Identification status: high confidence. I've seen a number of plants of this species in southern California, which are very similar in appearance. It keys readily to this id in McDougall 1964, p. 212:

1b.  Corolla not 2-lipped
3b.  Non-woody plants
42c. Heads radiate
99b. Pappus of bristles; no id in other branches
106a. Ray flowers purple
107b. Ray corollas narrow, not lobed at the tip
108a. Bracts of involucre in several series of different lengths
109b. Id not Townsendia, stemless daisy
111b. Stems over 4 inches tall
112b. Upper leaves not scalelike
113b. Leaves not spiny-toothed
114b. Bracts of involucre canescent (white-short-hairy) on back
119b. Bracts of involucre conspicuously many-ranked
121b. Bracts of involucre not glandular or sticky
122b. Leaves usually entire or with a few scattered teeth
123a. Stems 16 inches tall or less; leaves linear or nearly so... Machaeranthera canescens (=Aster canescens)

Determining in key element 99b that the pappus is of bristles can't be made from pictures of flowers; one need pictures of fruit, or must examine a split flower head with a hand lens. Fortunately, the other branches do not result in a match to these specimens. The species in the other branches almost all have white or yellow ligules except for Townsendia, stemless daisy, which is clearly not the determination since these plants definitely have stems. (It was easy to quickly determine this, since the next couplets in the key give you a choice between corolla yellow or corolla white.)

This is one of my all-time favorite species, producing those beautiful purple flowers at the end of summer, even in southern California without much summer rainfall at higher elevations. On the Bright Angel Trail in late summer, the displays of this species and the white prairie daisy, Symphyotrichum falcatum, are simply stunning.

I also love the way the name Machaeranthera rolls off the tongue. Try saying it three times - mack-ee-RAN-thur-uh - and see if you love it, too. ☺ Another attraction of the name is probably its similarity to the word Machiavellian.

By the way, I'm very displeased with the change in the name to Dieteria in the Flora of North America.

From a SEINet search, there are 25 vouchers of this species from the Coconino County portion of the Grand Canyon. The nearest is at: near El Tovar, with many vouchers given only at South Rim. Note that there may be additional vouchers at other herbaria not available through SEINet.

First occurrence on Bright Angel Trail: mile 0.00, elevation 6845 feet (2086 m).

Number of plants along Trail: This is a very common species along the upper part of the trail; at least 50 plants were found in at least 9 different locations in September 2007.


The plant in the next three pictures is at the trailhead, underneath the south side of the Quercus gambellii, whose leaves are also seen in the photos, from 5 September 2007, mile 0.00:

The plant in the next five pictures is from mile ~0.25, growing in a completely different environment:

The white on the back of the lower half of the phyllaries (bracts of the involucre) is due to very-short white matted hairs, similar to those on the stem just below the head. Hairs like these are called canescent, which accounts for the species epithet here.


See Resources for Grand Canyon Flora for further information on most of these references. Entries in the second column are either the name used in that source or a page reference. The name is linked to online pages when available. If a given reference does not contain this taxon, the entry is either left blank or contains a hyphen.

Scientific NameMachaeranthera canescens
1987 Grand Canyon Flora NameMachaeranthera canescens
1987 Grand Canyon Flora page34
SEINet Image PageMachaeranthera canescens
USDA PlantsMachaeranthera canescens
Flora of North AmericaDieteria canescens
Jepson Manual for California treatmentMachaeranthera canescens
Jepson Manual illustration page311
Kearney and Peebles NameAster canescens
Kearney and Peebles Page #873, 1072
Vascular Plants of AZ name
Vascular Plants of AZ volume: page
Huisinga et al 2006 name-
Huisinga et al 2006 page numbers-
Epple Name-
Epple description page #-
Epple pix #-
McDougall 1964 nameAster canescens
McDougall 1964 page #232
Brian 2000 Name
Phillips 1979 nameMachaeranthera canescens
Phillips 1979 page #120
Stockert 1967 nameAster canescens
Stockert 1967 page #24

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Copyright © 2007 by Tom Chester.
Permission is freely granted to reproduce any or all of this page as long as credit is given to me at this source:
Comments and feedback: Tom Chester
Last Update: 24 September 2007