Geranium of the Yellowstone Ecosystem

This is an effort to collect information I have researched regarding this genus. I am not an expert in Geranium, and welcome corrections/recommendations. My goal is to help learn and identify plants in the Greater Yellowstone Ecosystem. Geraniums are among the highest volume of “Needs ID” observations in this area. This maybe due to the challenges in distinguishing species.

Geranium viscosissimum (Sticky Geranium, Sticky Purple Geranium)

Photo 1 Source. Photo 2 Source

Range: All counties in the Greater Yellowstone Ecosystem
Observations in Flora of the Yellowstone Ecosystem Project
Identification Resources: USDA Plant Guide, American Southwest, Montana Field Guide,
Flowers are 1.5 inches in diameter with pink to purple petals and red to purple veins. The lower half of the petals are hairy. Plants are 1 - 3 feet tall. Sepals are only visible from below and end in short bristle (awn). Stems and leaves are covered with sticky hairs all over. G. richardsonii can also have pale pink flowers, but only has hairs on the veins on the lower side of its leaves. There are reports of viscossimum/richardsonii hybrids making distinguishing the species even more difficult.

Geranium richardsonii

Photo 1 Source. Photo 2 Source

Range: All counties in the Greater Yellowstone Ecosystem
Observations in Flora of the Yellowstone Ecosystem Project
Identification Resources: Montana Field Guide, Jepson herbarium, American Southwest
Flowers are 0.5 - 1.25 inches in diameter with white (sometimes pale pink) petals that have purple veins. The lower half of the petals are hairy. Plants are 1 - 3 feet tall. Bristle (awn) tipped sepals, shorter than the petals and may be seen between the petals. Stems are covered with glandular hairs. G. richardsonii only has hairs on the veins on the lower side of its leaves, unlike G. viscosissimum, which has leaves that are hairy all over. There are reports of viscossimum/richardsonii hybrids making distinguishing the species even more difficult.

Geranium caespitosum (Pinewoods Geranium)

Photo 1 Source Photo 2 Source

Range: within the GYE, only Sublette County
Observations in Flora of the Yellowstone Ecosystem Project
Identification Resources: Wildflowers of New Mexico, Yavapai County Native & Naturalized Plants, SEINet, Southwest Desert Flora, American Southwest
Leaves mostly basal, reduced opposite leaves on flowering stems. Leaf surfaces hairy to sparsely hairy, deeply lobed, equally toothed. Flowers variable and potentially similar to richardsonii and viscosissimum. Petals may be ovate, tapering at end or have a notch. They may or may not have dark veins. Flower characteristics more associated with caespitosum: backward drooping petals, arched stamens. Darker purple flowers with less visible petal veins in Sublette County WY should be evaluated for caespitosum.

Geranium bicknelli

Photo 1 Source-Note awn from sepals between petals. Photo 2 Source-Note flower pair and hairy sepals.

Range: Montana: All counties in GYE except Carbon. Wyoming: Park, Teton and Lincoln Counties. Idaho: Caribou, Madison Counties.
Observations in Flora of the Yellowstone Ecosystem Project
Identification Resources: Minnesota Wildflowers
Flowers are 1/3 inch across, egg shaped petals with notch at the tip. Flowers typically in pairs each attached to its own 0.75-1 inch peduncle. 5 hairy, elliptical sepals with a conspicuous sharp awn (bristle-like appendage).

Geranium carolinanium (Carolina Cranesbill)

Photo 1 Source Photo 2 Source

Range: Madison Co, ID; Fremont Co, ID; Madison Co, MT; Gallatin Co, MT
Identification Resources: Minnesota Wildflowers
Lance-elliptic sepals are longer than petals with sharp awn. Oblong petals are notched at tip. A pair of flowers grow on a single peduncle attached with a short (sometimes hidden) pedicel/stalk.

Other species to consider

Geranium molle (Dove’s-foot Crane’s-Bill): BONAP indicates rare presence in Gallatin County and Madison County MT. iNaturalist indicates this plant is out-of-range for this area. Currently there is only 1 observation in iNaturalist, in the Greater Yellowstone Ecosystem and it was not flowering at the time of the observation. Deep notches in petals, results in appearance almost of having 10 petals.
Geranium pusillum (Small-flowered Crane's-Bill): BONAP indicates rare presence in a few scattered counties in the GYE (indicating escaped ornamentals or otherwise invasive?). Currently there are no observation in iNaturalist, in the Greater Yellowstone Ecosystem. The petals are notched with uneven separation. The hairy sepals can be seen from the top of the flower where there are gaps in the petals.
Note to Self - research this introduced species: https://www.inaturalist.org/observations/149156595

Identification

Add Phenology annotations to Geranium - This is a great way to interact with these plants on iNat and add to the value of the data. You can read about phenology annotations in this post on the iNat forum.
Geraniums needing ID in Sublette County, WY (consider separate review because of potential for caespitosum): https://www.inaturalist.org/observations/identify?taxon_id=47701&place_id=1168
Geraniums needing ID in Greater Yellowstone Ecosystem: https://www.inaturalist.org/observations/identify?taxon_id=47701&project_id=144298
richardsonii script White flower, sepals visible from top of flower between petals. https://www.inaturalist.org/projects/flora-of-the-yellowstone-ecosystem/journal/72776-geranium-of-the-yellowstone-ecosystem

Posted on December 4, 2022 05:17 AM by

whitneybrook