Peniocereus

Peniocereus
File:Peniocereus greggii.jpg
Kingdom	Plantae
Family	Cactaceae
Subfamily	Cactoideae
Tribe	Phyllocacteae
SubTribe	Echinocereinae
Genus	Peniocereus
Species
Notes	Taxonomy follows Joël Lodé (2015) with reference to Arias et al. (2005), Hernández-Hernández et al. (2011), and Hunt (1998, 2000).

Etymology

The name means "tail cactus", referring to the long, slender, trailing stems.

Description

Peniocereus is a genus of shrubby cacti with thin, elongated stems and large underground storage roots.

• Habit: Shrubby; prostrate to semi-erect; often supported by surrounding vegetation.
• Stems: Slender, ribbed; up to ~4 m long; papillose or tomentose epidermis.
• Branching: Sparse; stems often appear filamentous.
• Roots: Tuberous or napiform; often very large relative to the plant.
• Spines: Small, fine, acicular; sometimes appressed.
• Growth form: Monomorphic (juvenile and adult stems similar).
• Flowers: Diurnal or nocturnal depending on species; large; self-sterile.
• Flower shape: Funnel-shaped with long, slender tube bearing bristles or spines.
• Flower color: Mostly white to off-white; sometimes red, pink, or purple.
• Pollination: By sphingid moths (Sphingidae) and hummingbirds.
• Fruits: Ovoid to pear-shaped; fleshy; bright red with red pulp; with bristles and deciduous spines.
• Seeds: Ovate; black; rough-textured.

Habitat

Occurs in a variety of arid to semi-arid environments:

• limestone and sandy soils
• alluvial plains
• rocky outcrops and cliffs
• deciduous dry forests
• shrublands and coastal zones

Often grows under or among shrubs (e.g. Larrea, Prosopis) for support and protection.

Altitude range: from sea level to ~1500 m.

Distribution

North America:

• Mexico (widespread across multiple states)
• United States (Arizona, southern New Mexico, southern Texas)

Taxonomy

A complex genus with significant redefinition based on molecular data.

Key points:

• Historically included taxa from Nyctocereus, Cullmannia, and Neoevansia
• Hunt & Taylor (1991): partial reclassification of Nyctocereus species
• Arias et al. (2005): demonstrated polyphyly of Peniocereus sensu lato
• Nyctocereus serpentinus separated again as a distinct lineage
• Subgenus Pseudoacanthocereus shown to belong within Acanthocereus
• Hernández-Hernández et al. (2011): confirmed paraphyly of expanded concept
• Strong phylogenetic link between some former Peniocereus taxa and Hylocereeae

Peniocereus sensu stricto is retained as a valid genus in Lodé (2015).

Species

According to Joël Lodé (2015):

• Peniocereus diguetii
• Peniocereus greggii
• Peniocereus hoockeanus (nom. inval.)
• Peniocereus johnstonii
• Peniocereus lazaro-cardenasii
• Peniocereus marianus
• Peniocereus striatus
• Peniocereus viperinus
• Peniocereus zopilotensis

Notes

• Notable for massive underground tuberous roots relative to small aerial stems.
• Often nearly invisible in habitat except during flowering.
• Large flowers contrast strongly with delicate stems.
• Represents a refined, restricted lineage after removal of unrelated taxa.
• Strong evolutionary links to Acanthocereus in excluded groups.