Plant Species of the Bright Angel Trail:
Cooper's rubberweed, Hymenoxys cooperi

Synonyms: Actinella cooperi, Hymenoxys cooperi var. canescens, Hymenoxys virgata. Other common names are Cooper's hymenoxys, bitterweed, Cooper's bitterweed, Arizona rubberweed, Arizona hymenoxys.

See Plant Guide to Bright Angel Trail for an introduction to this page, especially the Introduction To These Species Pages.


Identification status: Identification is highly probable, but not 100% since I can't check for the pappus or the receptacle chaff in my photographs and thus cannot key it out completely. Nothing else in McDougall seems to fit these plants, and this species is vouchered from this trail.

The keying in McDougall is:

1' Corolla not 2-lipped
3' Herbs
42'' Heads radiate
99'' Pappus of awns or scales (needs to be checked)
157' Receptacle without chaff (needs to be checked)
163' Ray flowers yellow
166' Leaves without oil glands
171 Leaves alternate
172'' Leaves with linear, entire lobes
175'' Ray flowers more than 5
176' Stems solitary or few
177' Leaf blades and lobes very narrowly linear ... H. cooperi

I originally made a mistake in determining this in September 2007, keying it to H. richardsonii under couplet element 176 Stems several or many, since my September 2007 pictures showed multiple stems. However, most of the plants in May 2008 had only a single stem, and none of them had conspicuous long hairs at the base. Also, H. richardsonii is a plant mostly of the pine forest, not the dry, rocky slopes where the plants here are found. Vouchers of H. richardsonii in this area of the Grand Canyon are all on the rims, and the 1987 Grand Canyon Checklist gives 6500 feet as its minimum elevation.

I spent considerable time on this determination, since the ligules on the plants in my 2008 photographs are depauperate versions of the ligules seen in online pictures, and because the 1987 Grand Canyon Checklist places this species only above an elevation of 7150 feet. However, after I couldn't find any other possible determination, I found that the type specimen for Hymenoxys virgata, a synonym for Hymenoxys cooperi, was taken from the Bright Angel Trail. Also, the ligules in my September 2007 pictures look normal size.

In fact, the 1987 Grand Canyon Checklist gives the Bright Angel Trail as a locality, even though the maximum elevation on the trail is 6845 feet. The lowest elevation voucher with a well-determined location from the Grand Canyon area is at 4600 feet, and Kearney and Peebles place it at 2000 to 7000 feet in all of Arizona.

See also pictures of this species from SEINet.

From a SEINet search on 18 May 2008, there are 16 vouchers of this species from the Coconino County portion of the Grand Canyon. The voucher from this trail was not found in that search (not all vouchers are online yet). Note that there may be additional vouchers at other herbaria not available through SEINet.

First occurrence on Bright Angel Trail: mile 1.82, elevation 5620 feet (2086 m); first off-trail plants at mile 0.53, elevation 6525 feet (1989 m).

Number of plants along Trail: at least 10 plants were found in at least different 2 locations in May 2008.


From 5 May 2008, mile 1.82. This plant is the one I was most concerned about being H. richardsonii due to the multiple stems. But the Flora of North America treatment says H. cooperi can have generaly 1-3 stems, and even up to 15 stems. This plant looks almost identical in every other respect to later plants on the trail.

From 6 May 2008, mile 3.00:

From 6 May 2008, from the horse trail just above the 3 mile resthouse:

From 5 September 2007, mile 0.53:

From 5 September 2007, mile 2.70:


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.

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Copyright © 2008 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: 18 May 2008