Plant Species of the Bright Angel Trail: hoary-aster, Machaeranthera canescens
See Plant Guide to Bright Angel Trail for an introduction to this page.
Characteristics
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.
Pictures
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.
References
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.
| Family | Asteraceae |
|---|---|
| Scientific Name | Machaeranthera canescens |
| 1987 Grand Canyon Flora Name | Machaeranthera canescens |
| 1987 Grand Canyon Flora page | 34 |
| SEINet Image Page | Machaeranthera canescens |
| USDA Plants | Machaeranthera canescens |
| Flora of North America | Dieteria canescens |
| Jepson Manual for California treatment | Machaeranthera canescens |
| Jepson Manual illustration page | 311 |
| Kearney and Peebles Name | Aster 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 name | Aster canescens |
| McDougall 1964 page # | 232 |
| Brian 2000 Name | |
| Phillips 1979 name | Machaeranthera canescens |
| Phillips 1979 page # | 120 |
| Stockert 1967 name | Aster canescens |
| Stockert 1967 page # | 24 |