Montana Field Guide

PLANTS: An annual that has erect stems and grows from 2 to 12 cm tall (Lesica et al. 2012). Plants are nearly hairless (glabrate) to glandular-puberulent. Plants are fibrous rooted or have a slender taproot. Sources: Giblin et al. [eds.] 2018; Lesica et al. 2012.

LEAVES: Leaves are simple, sessile, and arranged opposite on the stem. The leaf petiole is generally less than or equal to the length of the blade, about 2-10 mm long. Source: Lesica et al. 2012.

INFLORESCENCE: Showy yellow flowers grow on long stems (pedicels) from the upper leaf axils. Flowers are strongly bilabiate, petals flare open, and lowest petal is the longest. Source: Giblin et al. [eds.] 2018; Lesica et al. 2012.

The specific epithet ampliatus translates from Latin to “expanded” in reference to its expanded lower lip (Merriam-Webster 2019). Mimulus is derived from the Latin word mime, meaning “actor” or “mimic,” and the male diminutive -ulus (Merriam-Webster 2019). This is most likely referring to the mask-like appearance of the flowers.

Stalk-leaved Monkeyflower flowers in late June and early July (Nesom et al. 2012).

Montana specimens of Mimulus ampliatus have previously been incorrectly referred to as Mimulus patulus or Mimulus washingtonensis which do not occur in Montana (Lesica et al. 2012). Many past reports of M. floribundus were mis-identified and are actually Mimulus ampliatus.

Montana has 14 native Mimulus species (Lesica et al. 2012). The following species share characteristics of being short annuals, often less than 15 cm tall, with yellow flowers.

Stalk-leaved Monkeyflower-Mimulus ampliatus
*Hairs: Stems and calyx glabrate to glandular pubescent. Hairs are single-celled (not septate).
*Leaves: Petiolate. Blades are ovate, dentate, 2-10 mm long.
*Flower Stem: Pedicel is 2-3 times as long as the calyx.
*Corolla: 10-15 mm long, yellow, flares open, strongly bilabiate, and lower lip is longest.
*Calyx: Purplish, 4-8 mm long. Teeth (or lobes) equal, about 0.5 mm long.

Short-flowered Monkeyflower-Mimulus breviflorus
*Hairs: Stems and calyx with glandular-puberulent. Hairs are single-celled (not septate).
*Leaves: Petiolate, usually longer than the calyx. Blades are narrowly elliptic, entire, and 5-10 mm long.
*Flower Stem: Pedicel is 1-3 times as long as the calyx.
*Corolla: 5-8 mm long, yellow, and slightly bilabiate with subequal lobes.
*Calyx: 3-5 mm long. Teeth about equal, 1 mm or less long.

Floriferous Monkeyflower-Mimulus floribundus
*Hairs: Stems and calyx with glandular-villous, usually multi-cellular (septate), but occasionally unicellular hairs.
*Leaves: Petiolate, mostly shorter than the leaf blades. Blades are ovate, not noticeably dentate, and 4-12 mm long.
*Flower Stem: In fruit the pedicel ascends or is curved, and is not pressed against the substrate.
*Corolla: 7-11 mm long, yellow, bilabiate with a larger lower lobe and a red-spotted palate.
*Calyx: 4-7 mm long. Teeth equal, 1 mm or less long.

Thinsepal Monkeyflower-Mimulus hymenophyllus
*Stems are generally more prostrate and at the basal nodes are sharply bent.
*Hairs: Stems and calyx with sparsely glandular-pubescent. Hairs are single-celled (not septate).
*Leaves: Long-petiolate. Petiole is mostly longer than the blade. Blades are ovate, dentate, and 4-12 mm long.
*Flower Stem: Pedicel of flower is 3-4 times longer than the calyx. In fruit the pedicel bends to form about a 90-degree angle with stem and is generally pressed against the substrate.
*Corolla: 7-20 mm long, yellow, and nearly regular.
*Calyx: 3-5 mmm long. Teeth about equal with rounded to ovate tips. About 1 mm long.

Short-flowered Monkeyflower-Mimulus suksdorfii
*Hairs: Stems and calyx glabrate to glandular-puberulent. Hairs are single-celled (not septate).
*Leaves: Sessile. Blades are narrowly elliptic, entire, and 5-10 mm long.
*Flower Stems: Calyx about as long as the pedicel.
*Corolla: 5-8 mm long, yellow, and slightly bilabiate with subequal lobes.
*Calyx: Purplish, 3-5 mm long. Teeth about equal, 0.5 mm or less long.
*Habitat: In drier habitats than most Monkeyflowers.

Common Large Monkeyflower-Mimulus guttatus
*Plants found in temporarily moist areas, may grow as short annuals while those in permanently moist areas tend to be taller perennials; Sometimes plants become stoloniferous (Lesica et al. 2012).
*Hairs: Stems and calyx glabrate to glandular-puberulent. Hairs are single-celled (not septate).
*Leaves: Petiole is short. Blades are ovate, serrate, and 0.5-9 cm long.
*Corolla: 15-40 mm long, yellow with red-spots, and strongly bilabiate with spreading lips.
*Calyx: 6-14 mm long. Teeth (or lobes) acute, 0.5-3 mm long, and unequal; the upper calyx lobe is largest.

Stalk-leaved Monkeyflower prefers open seeps and vernally moist soil along slopes, cliffs and streams from the valleys to the subalpine zones in Montana (Lesica et al. 2012).

ASSOCIATED SPECIES
In the Pacific Northwest, Stalk-leaved Monkeyflower can be found in Ponderosa Pine (Pinus ponderosa) grasslands as well as commonly among Bluebunch Wheatgrass (Elymus spicatus) and Idaho Fescue (Festuca idahoensis) (Meinke 1995). Populations have also been found associated with Wiregrass (Ventenata dubia) (Meinke 1992).

POLLINATION
Based on its similarity to Mimulus washingtonensis it is presumed that Stalk-leaved Monkeyflower is pollinated by small, native, ground-nesting bees and bumblebees (Meinke 1995).

POLLINATORS
The following animal species have been reported as pollinators of this plant species or its genus where their geographic ranges overlap: Bombus vagans, Bombus bifarius, Bombus centralis, Bombus flavifrons, and Bombus pensylvanicus (Thorp et al. 1983, Colla and Dumesh 2010).

FLOWERS
Mature flowers of Stalk-leaved Monkeyflower have a 10 to 15 mm long yellow corolla that is bilabiate with a longer lower lip that is slightly deflexed from the upper (Lesica et al. 2012). The calyx is purplish and 4 to 8 mm long. The pedicel is 2 to 3 times as long as the calyx.

FRUIT
Mature fruit of Stalk-leaved Monkeyflower are ellipsoidal capsules, 3-6 mm long with many seeds (Lesica et al. 2012).

Across its range, it is presumed that Stalk-leaved Monkeyflower is sensitive to invasions by exotic grasses, particularly bromes (Bromus spp.) as well as presence of livestock (Meinke 1995). Individuals also are limited in their distribution by their dependence on a source of vernal moisture such as springs or seepages (Meinke 1995).

STATE THREAT SCORE REASON
Threat impact not assigned because threats are not known (MTNHP Threat Assessment 2021).