Trichomes with crystals in the Cephalocereus Pfeiff. areoles

This research describes the trichomes produced in the old vegetative areoles of the five species of Cephalocereus Pfeiff. Light and scanning electron microscopy and energy dispersive X-ray analysis were used to characterize the crystals present in the stem vegetative areoles far from the apical meristem. We are reporting for the first time for the Cactaceae family capitated trichomes with crystals. Crystals had diverse shapes (prismatic, styloid, sandy) and they all contain C as their principal element, as well as Na, Cl, Si, Mg, S, and Ca in different concentrations. Trichome and crystal characteristics allowed distinguishing the species of Cephalocereus. For example, capitate trichomes are shared by C. columna-trajani and C. senilis but differ because in C. columna-trajani there is one prismatic crystal per cell and sandy crystals in C. senilis. The other three species share non-capitated trichomes with prismatic crystals in the apical cell and styloids in the other cells. The species of Cephalocereus share the ontogenetic pathway of producing trichomes and spines in the areoles far from the apical meristem, suggesting that trichomes with crystals may be protecting the spines meristems.