The polymorphic weddellite crystals in three species of Cephalocereus (Cactaceae)

• Published in: Micron (Oxford, England : 1993) England : 1993), 2015-10, Vol.77, p.1-8
• Main Authors: Bárcenas-Argüello, María-Luisa, Gutiérrez-Castorena, Ma. C-del-Carmen, Terrazas, Teresa
• Format: Article
• Language: English
• Subjects: Biominerals; Botryoidal; Cactaceae - chemistry; Cactaceae - cytology; Cactaceae - ultrastructure; Calcium Oxalate - analysis; Cephalocereus apicicephalium; Crystal core; Crystalline classes; Crystallization; Inclusion Bodies - chemistry; Inclusion Bodies - ultrastructure; Mexico; Microscopy, Electron, Scanning; Spectrometry, X-Ray Emission
• ISSN: 0968-4328; 1878-4291
• DOI: 10.1016/j.micron.2015.05.014

•Weddellite crystals presented as both simple and aggregate in Cephalocereus species.•Calcium oxalate is associated with low concentrations of eight elements, and the polymorphism may be related to the edaphic environment in which these species grow.•The crystal nucleus presents particular optical properties and is made of Ca. Mineral inclusions in plant cells are genetically regulated, have an ecological function and are used as taxonomic characters. In Cactaceae, crystals in epidermal and cortical tissues have been reported; however, few studies have conducted chemical and morphological analyses on these crystals, and even fewer have reported non-mineral calcium to determine its systematic value. Cephalocereus apicicephalium, C. totolapensis and C. nizandensis are Cactaceae species endemic to the Isthmus of Tehuantepec, Mexico with abundant epidermal prismatic crystals. In the present study, we characterize the mineral cell inclusions, including their chemical composition and their morphology, for three species of Cephalocereus. Crystals of healthy branches of the three species were isolated and studied. The crystals were identified by X-ray diffraction (XRD), their morphology was described using a petrographic and scanning electron microscope (SEM), and their elemental composition was measured with Energy Dispersive X-ray (EDXAR). The three species synthesized weddellite with different degrees of hydration depending on the species. The optical properties of calcium oxalate crystals were different from the core, which was calcium carbonate. We observed a large diversity of predominantly spherical forms with SEM. EDXAR analysis detected different concentrations of Ca and significant amounts of elements, such as Si, Mg, Na, K, Cl, and Fe, which may be related to the edaphic environment of these cacti. The occurrence of weddellite is novel for the genus according to previous reports. The morphological diversity of the crystals may be related to their elemental composition and may be a source of phylogenetic characters.