Flora of North America species comparison

Delphinium nuttallianum represents an extremely difficult complex, with many variations in a number of morphologic traits. The complex has been and continues to be a major source of confusion for identification of Delphinium in North America. Type specimens of D. nuttallianum represent plants growing under dry conditions in open areas. These are typically found at 1200-2000 m in sage scrub or lower montane forest. Delphinium nuttallianum may be confused with D. andersonii, D. antoninum, D. depauperatum, D. gracilentum, and two subspecies of D. patens (subsp. patens and subsp. montanum). Features that may be used to separate D. nuttallianum from the first four, are enumerated under the respective species discussions. From D. patens subsp. patens, D. nuttallianum may be distinguished by its narrower leaf lobes, larger fruits, and more compact inflorescence. The frequent presence of glandular hairs in the inflorescence of D. patens subsp. montanum, contrasted with their absence in D. nuttallianum, will separate these taxa. Dwarfed plants of D. polycladon may be confused with D. nuttallianum. The latter, however may be distinguished by its ringed seeds, and it does not have prominent buds or sigmoid pedicel.

Hybrids have been seen between Delphinium nuttallianum and D. andersonii, D. depauperatum (D. ×burkei Greene), D. distichum (D. ×diversicolor Rydberg), D. nudicaule, and D. polycladon.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

At the sites in Manitoba and Saskatchewan, Delphinium glaucum is naturalized, not native.

Delphinium glaucum hybridizes extensively with D. barbeyi in Utah and Colorado to the extent that hybrids [D. ×occidentale (S. Watson) S. Watson] are more common in many areas than individuals of either parental stock. It occasionally hybridizes with D. distichum, D. polycladon, D. ramosum, and D. stachydeum. Hybrids with D. brachycentrum are called D. ×nutans A. Nelson.

Tremendous variation is apparent in what is here recognized as Delphinium glaucum. This is the northern expression of the complex described in the discussion under Delphinium subsect. Exaltata. Although some geographic patterns are apparent in the variation within D. glaucum, infraspecific entities are not here recognized. Apparently because of rather recent and/or incomplete genetic isolation, the degree of differentiation between these units is not such that they can be consistently recognized.

Specimens named Delphinium splendens represent plants grown in high-moisture, low-light conditions and may occur as sporadic individuals anywhere from California to Alaska. Type specimens of D. brownii Rydberg, D. canmorense Rydberg, and D. hookeri A. Nelson represent plants grown on relatively dry sites at high latitudes. Plants from dry sites at low latitudes are represented by D. bakerianum Bornmüller and D. occidentale var. reticulatum A. Nelson. Plants with lavender to white flowers are represented by type specimens of D. brownii forma pallidiflorum B. Boivin and D. cucullatum A. Nelson. Type specimens of D. alatum A. Nelson and D. glaucum var. alpinum F. L. Wynd (an invalid name) represent plants growing above or near treeline.

Delphinium glaucum may be confused with D. californicum, D. exaltatum, D. polycladon, or D. stachydeum. For distinctions from D. californicum, see discussion under that species. Absence of basal or proximal cauline leaves, generally much larger plants (greater than 1.5 m), more flowers in the inflorescence, and shorter petioles on the leaves of D. glaucum are features that serve to distinguish this species from D. polycladon. In the latter, the leaves are primarily on the proximal stem, plants often less than 1.5 m, flowers more scattered, and petioles more than twice the length of leaf blades. Features of the sepals may be used to distinguish D. glaucum (dark lavender to blue purple, usually only minutely puberulent) from D. stachydeum (bright blue, densely puberulent). Vegetative parts of D. stachydeum are also densely puberulent, while those of D. glaucum typically are glabrous.

(Discussion copyrighted by Flora of North America; reprinted with permission.)