Subdivisions

• Dudleya attenuata subsp. attenuata — Occurs in northern Baja California, with a small population in San Diego County in the Border Field State Park. The southern range of the diploid subspecies ends near El Rosario. A form occurs on the Punta Banda in Ensenada that is identical to a typical ssp. attenuata, but phylogenetic analysis has revealed that it is not sister to D. attenuata, instead being basal to Dudleya formosa and Dudleya edulis. This form is diploid or tetraploid, with 17 or 34 chromosomes.^[7] A second cytological form occurs near and around the coast of El Rosario, almost identical in appearance with a typical ssp. attenuata plant. The petals tends to be slightly longer than in diploids and floral parts slightly larger. This form is a tetraploid with 34 chromosomes, as opposed to 17.^[6][8]
• Dudleya attenuata subsp. australis — Caudex 4 to 8 mm thick. On the inflorescence, the pedicels are 2 to 12 mm long. On the flower, the corolla is white, but with some markings of red on the keel. Petals are 7 to 11 mm long, 3 to 4 mm wide. Subspecies australis is distinguished by its octoploid chromosome count. Chromosomes n = 68.^[6] Occurs along the coast of Baja California, from 50 miles south of El Rosario to near the village of Santa Rosaliíta.

Hybrids

This species hybridizes widely across its range. Parents of hybrids with Dudleya attenuata subsp. attenuata include D. candida, D. edulis, D. formosa, D. ingens, and D. variegata. A recurrent hybrid, known as D. × semiteres, is somewhat common compared to other crosses. The southern subspecies, Dudleya attenuata subsp. australis, is found hybridizing where Dudleya albiflora meets it in the south near Puerto Faro San José.^[9][6]

• Dudleya × semiteres (Rose) Moran — Occurs along the Pacific coast just north of Ensenada and on South Coronado & South Todos Santos islands. Caudex 1 to 3 cm thick, up to 15 cm high, branching to form clumps of 10 to 15 rosettes. Rosettes are 3 to 10 cm wide, of 15 to 30 ascending leaves. Leaves are green or glaucous, tapering uniformly with the sides roughly parallel in the bottom half. The leaves have a flattish or slightly convex ventral surface, and a convex dorsal surface, with the margins acute in the lower quarter of the plant but rounded towards the tip. Leaves are 3 to 10 cm long, 6 to 15 mm wide, and 3 to 6 mm thick.^[10] Peduncle is 10 to 30 cm tall, 3 to 8 mm thick. Bracts are deltate-lanceolate, acute, with the lowermost 1 to 3 cm long, 3 to 7 mm wide. The inflorescence is composed of typically 2 to 4 ascending branches, with each branch typically 3 to 10 cm long. 3 to 12 flowers are mounted on the pedicels, of which, the lowermost pedicels are 3 to 8 mm long.^[10] On the flower, the calyx is 4 to 5 mm wide, 4 to 6 mm high, segmenting into deltate-ovate to lanceolate sepals that are 3 to 5 mm long and 1.5 to 2 mm wide. Petals are white or cream, often with the keels lined in red, similar to D. a. subsp. attenuata. Petal shape is elliptic-oblong, acute, 8 to 10 mm long, 2 to 3.5 mm wide. The stamens are composed of filaments 5 to 6.5 mms long, with red or yellow anthers 1 to 1.5 mm long. The other presumptive parents of this recurrent hybrid are Dudleya brittonii and D. candida. × semiteres shares the chromosome count with its parents, having a chromosome number of n = 17.^[10]

Phylogeny

The taxonomic status of D. attenuata's subspecies is still under debate. Phylogenetic analysis reveals that although some specimens of D. attenuata from Punta Banda are sister to D. a. subsp. attenuata, other specimens collected are instead basal to D. edulis and D. formosa, illustrating the gene flow where the species overlap.^[7]