Southwest Colorado Wildflowers, Isocoma

Determining the identity of a species is dependent on the accuracy of the botanical key used. Unfortunately, the keys for the Four Corners area (and for other areas, I am sure) disagree far too often on species' characteristics and on what separates one species from similar ones. Consulting a number of floras and holding on to a good dose of doubt is frequently necessary; several floras and plenty of doubt are good to have regarding Isocoma species.

Descriptions in botanical keys of the two Isocomas shown on this page are in conflict on a number of plant characteristics. The descriptions of Isocoma rusbyi, for instance, vary widely from the Flora of North America to Intermountain Flora to Utah Flora to Colorado Flora. For example, FNA indicates that the leaves of Isocoma rusbyi are "not resinous"; Utah Flora indicates they are "resinous"; and Intermountain Flora says "glandular-glutinous".

FNA indicates that the phyllaries of Isocoma rusbyi are "sparsely or not at all gland-dotted, without resin pockets"; Utah Flora says the phyllaries have a thick... spot... [and are] resinous"; Intermountain indicates that the "involucre [is] glandular-glutinous or varnished" and is straw-colored except for the "green or greenish tip"; Colorado Flora does not mention these characteristics.

FNA indicates that I. rusbyi is found in "Rocky or sandy soils, sometimes in clay, usually saline, desert shrub communities, sometimes with scattered junipers"; Intermountain says "open hillsides and dry stream-beds"; Utah Flora indicates "riparian areas"; Colorado Flora says "desert-steppe , floodplains".

There are, of course, agreements on some aspects of the plants, but overall I certainly have some doubts about the identification of various Isocomas.

The genus was named by Thomas Nuttall in 1840. The name comes from the Greek which gives us "isos" for "equal" and "coma" for "mane" referring to the pappus hairs, which you can see gleaming white below the small, bulbous, individual flowers and above the green/yellow, pointed-tip phyllaries in the photographs below.

Isocoma pluriflora. Synonym: Haplopappus pluriflorus. (Many-flowered Jimmyweed, Many-flowered Goldenbush).
Asteraceae (Sunflower Family)

Semi-desert. Grasslands, openings along washes. Summer.
De-Na-Zin/Bisti Wilderness, New Mexico, August 5, 2007.

From a distance Isocoma pluriflora and Isocoma rusbyi (shown below) appear to be some form of Rabbitbrush, but a closer look shows flowers, stems, and leaves of a different structure. The plants are only about one or two feet tall. Both Isocomas shown on this page seem to prefer intermittently wet locations, primarily desert washes and road sides, but I have also seen them in drier semi-desert woodlands.

The species was first named Linosyris pluriflora by Torrey and Gray in 1842. It was renamed Isocoma pluriflora by Edward Greene. "Pluri" is Latin for "more, several", thus, "many-flowered".

Isocoma pluriflora. Synonym: Haplopappus pluriflorus. (Many-flowered Jimmyweed, Many-flowered Goldenbush).
Asteraceae (Sunflower Family)

Semi-desert. Grasslands, openings along washes. Summer.
De-Na-Zin/Bisti Wilderness, New Mexico, August 5, 2007.

Isocoma pluriflora. Synonym: Haplopappus pluriflorus. (Many-flowered Jimmyweed, Many-flowered Goldenbush).
Asteraceae (Sunflower Family)

Semi-desert. Grasslands, openings along washes. Summer.
De-Na-Zin/Bisti Wilderness, New Mexico, August 5, 2007.

Leaves on plants I found in De-Na-Zin were almost all prominently toothed; very few early leaves were entire. The Flora of North America indicates that I. pluriflora is "sometimes shallowly toothed" toward the tip.

The bright green leaves at left are the first leaves of early spring; they will darken with age.

Isocoma rusbyi. Synonym: Haplopappus rusbyi. (Rusby's Jimmyweed, Rusby's Goldenbush).
Asteraceae (Sunflower Family)

Semi-desert. Grasslands, openings along washes, roadsides. Summer, Fall.
Cannonball Mesa Road, September 2, 2007.

Isocoma rusbyi is woody-based with stiff, straw-colored stems supporting masses of golden-yellow disk flowers. Leaves are hairless but they can be glistening resinous, as can the phyllaries. In late summer and early fall, roadsides can have large clusters of these plants.

Henry Rusby discovered this species in Holbrook, Arizona (probably in 1883) and Edward Greene named it Isocoma rusbyi in 1906. Arthur Cronquist renamed it Haplopappus rusbyi in 1994. (More biographical information about Rusby.)

Isocoma rusbyi. Synonym: Haplopappus rusbyi. (Rusby's Jimmyweed, Rusby's Goldenbush).
Asteraceae (Sunflower Family)

Semi-desert. Grasslands, openings along washes, roadsides. Summer, Fall.
Cannonball Mesa Road, September 2, 2007.

Leaves are long and narrow, gray-green, and sessile. Stems are stiff, straw-colored, and have long longitudinal striations (visible with a 10 power hand lens).

Isocoma rusbyi. Synonym: Haplopappus rusbyi. (Rusby's Jimmyweed, Rusby's Goldenbush).
Asteraceae (Sunflower Family)

Semi-desert. Grasslands, openings along washes, roadsides. Summer, Fall.
Cannonball Mesa Road, September 2, 2007.

Species present in state and native
Species present in state and exotic
Species not present in state

County Color Key

Species present and not rare
Species present and rare
Species extirpated (historic)
Species extinct
Species noxious
Species exotic and present
Native species, but adventive in state
Eradicated
Questionable presence

Range map for Isocoma pluriflora

Range map for Isocoma rusbyi