Peniocereus

Peniocereus was first described in 1905 by Alwin Berger as a subgenus of Cereus with a single species, Cereus greggii. This taxon was elevated to the genus level as Peniocereus greggii by Britton and Rose in 1909. Later in 1974 an infrageneric classification was constructed based on morphological features that split Peniocereus into two subgenera: Peniocereus and Pseudoacanthocereus. In 2005 a molecular phylogenetic study of the genus supported this split and showed that Peniocereus is not monophyletic. ==Species==

Species include: ===Peniocereus sensu stricto=== Molecular phylogeny supported the position of this subgenus within Echinocereeae. ==Formerly included species==

Nyctocereus The 2005 molecular study showed that P. serpentinus is in Echinocereeae along with subgenus Peniocereus, but suggests resurrecting the monotopic Nyctocereus as it is sister to Bergerocactus. Subgenus Pseudoacanthocereus (Now Acanthocereus) Molecular phylogeny and morphological evidence suggests this subgenus is more closely related to Acanthocereus. ==References==