Delphinium (Larkspurs) of the Greater Yellowstone Ecosystem

I am a hobby naturalist seeking to improve my understanding of plant identification in my local region. I started this post as a way of collecting my notes on Delphinium. I have seen that there are large numbers of Delphinium in the area that have not been identified to research grade and I was hoping to learn how to improve them. What I have learned is that they are challenging to identify and in some cases, scientists are still determining morphological descriptions and ranges. While the notes below my not be that useful, I will keep them and continue to add to them should I learn something new.

Resources for Delphinium

Delphinium anatomical features

Roots and Bloom Structure of Cultivated Delphiniums has excellent diagrams. Even though it is focused on cultivated delphiniums, I think it is useful.
Pedicel: thin stalk connecting flowers to stem. Pedicel angle may result in columnar (straight up and down) or pyramidal arrangement of blossoms
Bracteoles: small reduced leaves on the pedicel behind the flower
Sepals: have the appearance of outside “petals” of the flower
Spur: tube-like extension from the back of the top sepal. This is present on all delphiniums and is useful for identification to genus.
Petals: the true petals are smaller and at the center of the blossom. The two top petals are fused.
Dissected leaves: lobed leaves. Note pointed or rounded tips and well as the width of the lobes. Note whether leaves are only basal or if some stem leaves are present.

Delphinium bicolor (Low Larkspur, Little Larkspur)

Photo 1 source Photo 2 Source

Range: All counties in Greater Yellowstone Ecosystem
Observations in Flora of the Yellowstone Ecosystem Project
Observations with descriptions and discussion: June 8, 2018 AB Canada, June 9, 2018 Gallatin County, June 14, 2009 Gallatin County
Identification Resources: Montana Field Guide, Saskatchewan Field Guide, eFloras, FNA
Distinctive features: shorter than other local larkspur; rounded leaves dissected into thin linear segments, mostly basal. Upper petals white with blue markings. Distinguish from nuttallianum by noting presence of small cleft (< 2mm) in lower petals, also lower sepals longer than the others (thanks to @plachuff for providing help here).

Delphinium nuttallianum (Nuttall’s larkspur, twolobe larkspur)

Photo 1 source. Photo 2 Source

Range: All counties in Greater Yellowstone Ecosystem
Observations in Flora of the Yellowstone Ecosystem Project
Identification Resources: Montana Field Guide, Southwest Colorado by Wildflowers, Larkspurs of the Columbia River Gorge of Oregon and Washington, US Forest Service Plant of the Week, Jepson Herbarium.
Distinctive features: similar in appearance to D. bicolor, but taller with more blooms and later blooming. Pyramidal inflorescence and lower flowers shorter than pedicel. Some observers have used exposed stamens as a means of distinguishing from bicolor, but this may not be reliable (see discussion on this observation ).

Delphinium geyeri (Geyer’s Larkspur, Plains Larkspur)

Photo source

Range: Park, WY; Fremont WY; Sublette,WY; Lincoln, WY; Fremont, ID. Rare in: Gallatin, MT and Carbon, MT.
Observations in Flora of the Yellowstone Ecosystem Project
Identification Resources: Eastern Colorado Wildflowers, Montana Field Guide
Distinctive Feature: bushy appearance from many stems, flowers more true blue than purple

Delphinium occidentale (duncecap larkspur, Subalpine Larkspur, Tall Mountain Larkspur)

Photo 1 source. Photo 2 Source

Range: All counties in Greater Yellowstone Ecosystem
Observations in Flora of the Yellowstone Ecosystem Project
Identification Resources: Montana Field Guide, Montana Plantlife, Burke Herbarium, JSTOR
Occidentale is potentially confused with glaucum and glaucenscens because they are all tall, have similar shaped flowers and their range is in delays.
Distinctive Features: Tall. More narrow/elongated blossoms. Traits that might distinguish occidentale from other tall larkspurs, such as glaucum are not fully agreed upon. Options include: pedicel length from mid inflorescence, follicle pubescence, and lower petal width.

Add note for glaucum and glaucescens.

Identification Workflows

Add Phenology annotations to Delphinium - 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.
Identify Delphinium in the Greater Yellowstone Ecosystem, excluding those you have previously reviewed
Identify Delphinium in the Greater Yellowstone Ecosystem, including those you have previously reviewed. When I have new knowledge, I sometimes like to revisit plants that Need IDs that I may have skipped over.