Name and distribution
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 et al. 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 et al. 2016, PDF pp. 2]
Growth form and reproductive maturity
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 et al. 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 et al. 2016, PDF pp. 4–6, 9]
Cephalium anatomy 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 et al. 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 et al. 2016, PDF pp. 6–9]
Crown development
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 et al. 2016, PDF pp. 9]
Related articles
Materials from the author's archive
The species also appears in Konrad Szychowski's private material archive. [Kaktusy i Inne 2006a, file p. 36, 37]
Synonyms and names in the literature
Backebergia chrysomallus · Backebergia militaris · Cephalocereus chrysomallus · Cephalocereus militaris · Cereus chrysomallus · Cereus militaris · Cereus militaris var. californicus · Mitrocereus chrysomallus · Pachycereus chrysomallus · Pachycereus militaris · Pilocereus chrysomallus · Pilocereus militaris [2-WWW]