Flora of North America species comparison

Hybrids between Delphinium cardinale and D. parryi have been named D. ×inflexum Davidson. Because of horticultural interest in red-flowered delphiniums, garden hybrids have been made with D. elatum, D. hesperium, D. hutchinsoniae, D. nudicaule, D. parishii, D. penardii, D. scopulorum, D. tatsienense Franchet, D. uliginosum, and D. zalil Aitchison & Hemsley, although D. cardinale does not grow with any of these in the wild.

Plants of Delphinium cardinale are quite variable in size, leaf distribution, and pubescence, resulting in considerable differences between, and sometimes within, populations. No patterns could be seen, however, to justify recognition of separate taxa within D. cardinale. Populations farther south (in Baja California, Mexico) may represent a distinct entity; they require further study.

The only possible confusion between Delphinium cardinale (seeds not ringed, fruits erect, grows in relatively dry sites) and another taxon might occur with Delphinium nudicaule (seeds ringed, fruits spreading, grows in moist habitats). The two are separated geographically and phenologically (although D. cardinale may begin flowering in southern California before D. nudicaule has finished in northern California).

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

Delphinium gracilentum hybridizes with D. patens subsp. patens in the northern Sierra Nevada foothills and is very similar to that species, making hybrids difficult to discern. While D. gracilentum and D. patens are easily distinguished in most of their ranges, morphologic distinctions between the two taxa are blurred in the northern Sierra Nevada foothills region, particularly in Butte County, California. Coniferous woods are preferred by D. gracilentum; D. patens subspp. patens and hepaticoideum are more often found in broadleaf woods. The former species has more widely spreading pedicels than the latter, and D. gracilentum usually has wider leaf lobes than D. patens subsp. patens. In the southern Sierra Nevada, D. gracilentum may come in contact with D. patens subsp. montanum. Though hybrids are not common, some gene flow has apparently occurred.

Sepal color phases are not stable and considerable variation occurs within populations. The type specimen of Delphinium gracilentum represents the northern, lower elevation, nonglandular, dark-flowered phase. The type specimen of D. gracilentum forma versicolor Ewan differs only by its pink or white flowers. A limited range of intermediate colors occurs, and populations may be made up of plants of a single color or several different colors. The type specimen of D. greenei Eastwood represents the southern, higher elevation, glandular (at least on pedicels) expression. The type specimen includes representatives of dark- and light-flowered individuals of this phase. The type specimen of D. gracilentum forma versicolor (not seen by the author) is the "albino" phase referred to by Greene in his description of D. gracilentum. Several of the paratypes cited by Ewan have been seen, as have a number of individuals in natural populations.

Delphinium gracilentum has been confused with D. patens or D. nuttallianum. Delphinium gracilentum may be distinguished from D. nuttallianum by its wider leaf lobes, smaller fruits, and more elongate inflorescences, and from D. patens by its wider leaf lobes, more open inflorescences, and usually shorter fruits.

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