Taxonomically, this species is an insular segregate of Dudleya caespitosa,[4] and was placed as a stopgap taxon by Reid Moran in his 1951 thesis on the genus.

[5] It is a member of the subgenus Dudleya, as it cannot be propagated from leaf cuttings, does not grow from a corm, and has tight petals.

The base of the leaf is generally 1 to 3 cm wide, and may wound red or yellow when detached from the stem.

[5][4] As defined by botanist Reid Moran, this species is an insular segregate of the Dudleya caespitosa complex.

In their 1903 work on the North American Crassulaceae, Joseph Nelson Rose and Nathaniel Lord Britton circumscribed the genus Dudleya.

The specific epithet of D. regalis is a reference to the name of the island, and also due to their "regal" appearance described by Johansen.

[10] In 1935, Johansen named Dudleya echeverioides based on specimens collected in 1930 by the late Hoffmann on Santa Rosa Island.

Johansen recognized D. echeverioides as being unusually distinct based on the sweetly-scented flowers, that he described as having an odor "unmistakably resembling that of woodland violets."

[11] Reid Moran, working on the taxonomy of the genus for his 1951 dissertation, revisited several of the new plants named by Johansen.

Moran recognized that D. regalis differed from D. hoffmannii with its narrower green leaves, more complex inflorescences, and more spreading petals.

[7] Plants matching the description of the odorous flowers of D. echeverioides could not be located by Moran, and with an apparent loss of the type specimen and a lack of an illustration, the original description made no distinction as to why the plant would be morphologically different from D. greenei.

[7] Although Moran kept D. greenei alive as a taxon as "a matter of temporary convenience," he never published his 1951 dissertation,[7] and thus this species has remained valid into the 21st century.