Calcium oxalate crystal macropattern and its usefulness in the taxonomy of Baccharis (Asteraceae)

Abstract

This study provides a comprehensive account of the various types of calcium oxalate crystals found in the genus Baccharis and assesses the exceptional value of crystal macropatterns for the taxonomy of the genus. The morphotype, occurrence, and chemical composition of the crystals found in the stems and leaves are studied. The 44 species included in this study were selected based on a broad phylogeny‐based sampling covering seven subgenera and 31 sections. These species were chosen to represent all the main phylogenetic lineages of Baccharis; thus, the sampling also represents a comprehensive coverage concerning evolutionary significance for such a large and environmentally and economically important plant group. The samples were analyzed by light microscopy, scanning electron microscopy (SEM), and energy‐dispersive x‐ray spectroscopy (EDS). Several morphotypes of crystals, including druses, crystal sand, styloids and prisms, were present. Based on their chemical composition, the crystals were classified as pure calcium oxalate, mixtures of oxalates and sulfates, and mixtures of oxalates, sulfates, and silica. The crystal macropatterns observed in this study aid in species identification and provide novel data for the taxonomy of Baccharis. Research Highlights Most species of Baccharis have a specific crystalline pattern. Each species produces a crystal morphotype or a set of morphotypes specific to it. The crystals observed are formed by calcium oxalate.

Leaf Epidermal Features for Differentiating Cecropia pachystachya Trécul from its Adulterant Tetrapanax papyrifer (Hook.) K. Koch

“…and Peumus boldus Molina), just by observing the micromorphology of the trichomes [20]. In addition, other anatomical markers have been evidenced in order to characterize and differentiate species, such as crystal morphotypes [21,22].…”

Comparative Anatomy of Ilex paraguariensis "Erva-Mate" and its Adulterant Citronella gongonha "Falso-Mate”

“…Amorphous crystals (Figure 5a) were found only in C. gongonha, whereas I. paraguariensis had prismatic crystals (Figure 5b, c). Crystal macropattern can be used to differentiate and identify species, as observed in a recent study by Raeski and coauthors [19].…”

“…It is important to highlight that Citronella gongonha possesses amorphous crystals on the epidermis and in the EDS analysis, manganese was found in its composition, beyond calcium oxalate. Several studies have been developed focusing on crystals, evaluating and differentiating crystals by type and chemical composition [15,16,19]. FESEM photographs and EDS analyses are shown in Figure 5 and Figure 6, respectively.…”

Anatomical features of ecological importance and taxonomic value revealed by scanning electron microscopy and light microscopy in Camonea umbellata (L.) A.R. Simões & Staples (Convolvulaceae)

“…Anatomical studies are very relevant because they unravel key traits that help differentiate species (Cutter, 2002;Metcalfe & Chalk, 1950;Stuessy, 2009). A number of recent studies have reported the importance of microscopic features in, for example, the authentication and quality control of species of ethnomedicinal interest and in taxonomy (Antunes et al, 2023;Raeski et al, 2023). In the case of Convolvulaceae, anatomical studies have provided valuable data to support the taxonomy of the family.…”