Flowering changes the apex
A densely hairy flowering region called a cephalium develops at the tips of mature branches of Mitrocereus militaris. Vázquez-Sánchez and colleagues studied the plant as Backebergia militaris. The current POWO checklist accepts Mitrocereus militaris. Its native range is southwestern Mexico, and it is introduced in Honduras. [Vázquez-Sánchez et al. 2016, Vázquez-Sánchez i wsp. 2016, PDF pp. 1–2, POWO 12.10.2026][2-WWW]
The researchers collected six cephalium-bearing branches from four plants in Michoacán. Their material ranged from the onset of yellow bristle formation to older regions with dark basal parts. They compared these with vegetative branches using anatomical sections. This series allowed them to reconstruct structural changes from the apex towards older tissues. [Vázquez-Sánchez et al. 2016, Vázquez-Sánchez i wsp. 2016, PDF pp. 2]
The areoles become crowded
On a green branch, the areoles are separated by portions of the ribs. In the cephalium, the spaces between them disappear and their arrangement becomes helical. Numerous hairs, bristles and spines conceal the surface. The botanical term phyllotaxis describes the arrangement of such repeated organs around an axis. A change in this pattern accompanies the transition to the reproductive region. [Vázquez-Sánchez et al. 2016, Vázquez-Sánchez i wsp. 2016, PDF pp. 2–5]
The dense covering is the visible part of this reorganisation. Within the cephalium, the thickness of the cell layer beneath the epidermis and the abundance of vascular bundles and mucilage cells also change. In the studied material, the apical region contained more cortical bundles than the corresponding part of a vegetative branch. The authors related this organisation to the specialisation of the flower- and fruit-bearing region. [Vázquez-Sánchez et al. 2016, Vázquez-Sánchez i wsp. 2016, PDF pp. 4–6, 9]
Green tissues and ageing
Near the apical meristem, the cephalium retains stomata and parenchyma containing chloroplasts. Its anatomy therefore permits photosynthesis in the young region. The extent of this process requires physiological measurements. The comparison included published information on Melocactus intortus, whose cephalium has a different complement of tissues. The cephalia of different cacti retain their own anatomical characteristics. [Vázquez-Sánchez et al. 2016, Vázquez-Sánchez i wsp. 2016, PDF pp. 7–11]
After flowering and fruit maturation, the areole is sealed by a periderm, a secondary protective tissue. It develops from dividing epidermal cells. In the older cephalium, the researchers also observed collapse and necrosis of cortical and pith cells. Darkening of the covering accompanied these changes. Living parenchyma cells nevertheless remained around the vascular bundles. [Vázquez-Sánchez et al. 2016, Vázquez-Sánchez i wsp. 2016, PDF pp. 6–9]
Branches renew the flowering regions
The plant grows sympodially, with successive parts of the crown formed by new branches. Each can eventually enter the cephalium-forming phase. The authors proposed that branch renewal helps maintain a balance between green vegetative surfaces and specialised flowering regions. This interpretation is linked to the observed architecture and requires further functional investigation. [Vázquez-Sánchez et al. 2016, Vázquez-Sánchez i wsp. 2016, PDF pp. 9]
The description of the cephalium helps identify reproductive maturity and interpret the history of older stem portions. In Mitrocereus militaris, hairs, areole arrangement, green tissues and periderm form a changing system. The study shows how a single apical meristem can produce regions with different functions during successive developmental phases. It adds an internal developmental process to the description of growth form. [Vázquez-Sánchez et al. 2016, Vázquez-Sánchez i wsp. 2016, PDF pp. 9–11]
Comparative morphology and anatomy of Backebergia militaris (Echinocereeae–Cactaceae) cephalium
Vázquez-Sánchez M., Terrazas T., Arias S., Comparative morphology and anatomy of Backebergia militaris (Echinocereeae–Cactaceae) cephalium, Plant Systematics and Evolution, 2016, 302(3):245-256, doi: 10.1007/s00606-015-1256-4
Morphology and anatomy of the Mitrocereus militaris cephalium, comparison with vegetative branches and changes associated with flowering and ageing.
Plants of the World Online — Royal Botanic Gardens, Kew
Accepted names, synonyms and distribution. A citation beside a taxon leads to its record.
Accessed 2026-10-08.