Cephalocereus

Growth form and shared characters

The genus Cephalocereus comprises cacti with elongated, ribbed stems, ranging from branching shrubs to tree-like plants. Species differ in the number and position of branches, spine density and the appearance of the mature shoot apex. The genus is native to Mexico. Individual species occupy dry scrub and seasonally deciduous forest. [Tapia et al. 2017] [2-WWW]

Two structural characters support the common ancestry of this group in the 2017 analysis. Prismatic crystals occur in the epidermis and the tissue beneath it. A woody cap formed from perianth remnants persists on the fruit. Their significance was established by comparison with related groups and reconstruction of character changes on the phylogenetic tree. [Tapia et al. 2017]

Different forms of the flowering region

In Cephalocereus senilis and C. columna-trajani, flowers develop in a lateral cephalium, a permanently modified part of the shoot. Areoles enlarge and become more closely spaced, while dense hairs and bristles cover the reproductive region. Its tissues lose chloroplasts and form periderm early. The remaining green part of the stem retains the organization of the vegetative region. [Tapia et al. 2017] [Vázquez-Sánchez et al. 2005]

Plants formerly assigned to Neodawsonia have a different organization. Their apical flowering region is termed a pseudocephalium. In species formerly placed in Neobuxbaumia, flowers appear without equally extensive modification of the reproductive region. This variation is useful for identifying plants. Abundant hairs near the flowers should be considered together with the position and anatomy of the region. [Tapia et al. 2017]

Shared ancestry and current names

Tapia and colleagues compared seven plastid DNA regions with external and anatomical characters. The former boundaries of Cephalocereus, Neobuxbaumia and Pseudomitrocereus cut across the recovered lineages. The authors united them within a single genus under the oldest name, Cephalocereus. A particularly close relationship united C. tetetzo with C. senilis and C. columna-trajani, despite their conspicuously different reproductive regions. [Tapia et al. 2017]

Species circumscriptions have also changed since that revision. In POWO, checked on 16 October 2026, C. nizandensis and C. totolapensis are synonyms of C. apicicephalium, while C. multiareolatus is a synonym of C. mezcalaensis. The historical names remain useful for finding publications and establishing which populations were studied. Observations recorded under a narrower name retain their original scope. [2-WWW] [2-WWW]

Habitats and interactions with neighbouring plants

Bedrock and local water conditions differentiate these cacti’s habitats. In the Tehuantepec basin, the studied populations of the C. apicicephalium group grew on calcareous rocks as well as substrates derived from andesite and metamorphic rocks. Cracks, rock cavities and accumulation of fine material also influenced their distribution. A description of one locality therefore applies to a particular population and its microhabitat. [Bárcenas-Argüello et al. 2010] [2-WWW]

In C. tetetzo, the association with the shrub Mimosa luisana spans different life stages. The sheltered microhabitat favours survival of the young cactus. In a field experiment, labelled water introduced into an adult cactus reached the neighbouring shrub. Separate species accounts connect such findings with the appropriate material, locality and developmental stage. [Valiente-Banuet and Ezcurra 1991] [Montesinos-Navarro et al. 2019]

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