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    When the two species shown on this page are first observed in the field, they do look quite similar, but a careful examination shows distinctive characteristics.

1) Erythranthe rubellus is a more robust species than Erythranthe suksdorfii:
Height: 1-22 cm tall versus 1-7 cm tall.
Pedicels: 7-18 mm long versus 2-7.
Calyx: 4-7 mm long versus 3-5 mm.
Calyx lobes .5-1 mm long versus .2-.7 mm.
Corolla: 6-8 mm long versus 4-6.5 mm.

2) The calyx lobes of Erythranthe rubellus are ciliate (one flora indicates "usually ciliate"), those of E. suksdorfii are not. Unfortunately, I did not get a photograph showing this detail.

3) E. rubellus grows in an open, unbranched pattern; E. suksdorfii grows in a compressed, much branched pattern.

4) As pointed out below:
E. rubellus leaves are usually entire but may be denticulate and they are usually shorter than the internodes; E. suksdorfii leaves are entire and they are longer than the internodes.
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    Guy Nesom and several co-authors published "A TAXONOMIC CONSPECTUS OF PHRYMACEAE", removing most species from the genus Mimulus and placing them in Erythranthe. See also Nesom 2012, "TAXONOMY OF ERYTHRANTHE SECT. SIMIOLA (PHRYMACEAE) ".

    "Erythranthe", is from the Greek, "erythros", red, and "anthos", flower. 

    Genetic research has shown that Erythranthe species belong in the Lopseed Family (Phrymaceae), not in the Snapdragon Family (Scrophulariaceae).

Erythranthe rubella
Erythranthe rubella

Erythranthe rubellus. Synonym: Mimulus rubella. (Redstem Monkey Flower)
Phrymaceae (Lopseed Family)
Synonym: Scrophulariaceae

Semi-desert, foothills, montane. Openings, shrublands, woodlands. Spring.
Above and left: Holly Trail, Hovenweep National Monument, Colorado, April 23, 2019.

At first I identified the species shown in the photographs above and to the left as Erythranthe suksdorfii. Superficially their flowers and leaves do look like those of E. suksdorfii, their elevation and soils are the same, and they are relatively near the E. suksdorfii shown below. However, when I took a closer look at the photographs several years after I took them, I realized my mistake. The photographs above and to the left show Erythranthe rubellus, not Erythranthe suksdorfii.

As noted at the top of the page, there are a significant number of morphological differences in the two species. Overall, E. rubellus is a more robust species than E. suksdorfii.

Comparing the corollas of the two species we find that those of E. rubellus are longer and more prominent: 6-8 mm long versus 4-6.5 mm for E. suksdorfii and they are often more exserted from the calyx, typically 2-9 mm versus 2-4 mm for E. suksdorfii.

Both species are uncommon in the Four Corners states and both occur over a wide elevation range, not agreed on by various botanists. I think it safe to say that they are found from the high desert elevations to the montane, from perhaps as low as 3,000 feet to as high as 9 or 10,000 feet. Although they both can be found in xeric woodlands and shrublands, E. rubellus can be found in washes (as in the case of the plants at left) and similar seasonally moist areas.

Erythranthe rubella

Erythranthe rubellus. Synonym: Mimulus rubella. (Redstem Monkey Flower)
Phrymaceae (Lopseed Family)
Synonym: Scrophulariaceae

Semi-desert, foothills, montane. Openings, shrublands, woodlands. Spring.
Holly Trail, Hovenweep National Monument, Colorado, April 23, 2019.

The photograph at left shows two key characteristics that separate E. rubellus from E. suksdorfii

1) Leaves are shorter than the internodes (the distance between the closest two places on the stem from which the leaves or stems emerge, as pointed to by the red arrows). Leaves of E. suksdorfii are longer than the internodes.

2) Some leaves of E. rubellus are denticulate, i.e., they have a slight tooth-like projection, as shown in the two leaves the white arrows point to. Leaves of E. suksdorfii are entire; they have smooth margins without teeth.

 

Mimulus suksdorfii

Erythranthe suksdorfii. Synonym: Mimulus suksdorfii. (Suksdorf's Monkey Flower)
Phrymaceae (Lopseed Family)
Synonym: Scrophulariaceae

Semi-desert, foothills, montane. Openings, shrublands, woodlands. Spring.
Near Hovenweep National Monument, Colorado/Utah border, April 18, 2010.

This Monkey flower is thought to be uncommon in the Colorado Plateau region that this website covers. It is quite a minute plant, ranging from 1-7 centimeters tall and is thus quite difficult to spot from the height of a human, which may be why it is thought to be uncommon. Perhaps it is there but unnoticed. Betty and I find it more and more often. Its attractive yellow flower is what catches our eyes -- when we are walking at a snail's pace.

Erythranthe suksdorfii is found from about 4,000 to 8,000 feet elevation in the Four Corners region, usually in exposed areas of sagebrush, Pinyon/Pine, and Ponderosa communities, and in Welsh's words, "often along windswept ridges", but all the photographs on this page show plants in sandy flatlands. We have also found it in far western San Juan National Forest in Ponderosa communities. Farther east in Colorado, E. suksdorfii has been found at 10,000 feet.

This species was first named Mimulus suksdorfii by Asa Gray in 1886 from a specimen collected "on rocks Mount Paddo" in Washington in 1885 by Wilhelm Suksdorf (1850-1932, Gray's respected collector in Washington). (Click for more biographical information about Suksdorf).

Mimulus expert Guy Nesom and several co-authors published a rearrangement of the Mimulus genus, removing most species from Mimulus and placing them in Erythranthe. See also Nesom 2012."Erythranthe", is from the Greek, "erythros", red, and "anthos", flower. 

Genetic research has shown that Erythranthe species belong in the Lopseed Family (Phrymaceae), not in the Snapdragon Family (Scrophulariaceae).

Mimulus suksdorfii

Erythranthe suksdorfii. Synonym: Mimulus suksdorfii. (Suksdorf's Monkey Flower)
Phrymaceae (Lopseed Family)
Synonym: Scrophulariaceae

Semi-desert, foothills, montane. Openings, shrublands, woodlands. Spring.
Near Hovenweep National Monument, Colorado/Utah border, April 18, 2010.

Sand is stuck to the sticky glandular hairs on the stem, leaves, and re-ribbed calyx.

The corolla is minute, only 4-6.5 mm long and it drops soon after fully opening.

Mimulus suksdorfii

Erythranthe suksdorfii. Synonym: Mimulus suksdorfii. (Suksdorf's Monkey Flower)
Phrymaceae (Lopseed Family)
Synonym: Scrophulariaceae

Semi-desert, foothills, montane. Openings, shrublands, woodlands. Spring.
Near Hovenweep National Monument, Colorado/Utah border, April 25, 2010.

Range map © John Kartesz,
Floristic Synthesis of North America

State Color Key

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

Erythranthe rubella

Range map for Erythranthe rubellus

Erythranthe suksdorfii

Range map for Erythranthe suksdorfii