Systematic review on raphide morphotype calcium oxalate crystals in angiosperms

Area of Science:

• Plant Biology
• Biomineralization
• Plant Anatomy

Background:

• Calcium oxalate (CaOx) crystals are biominerals formed during a biomineralization process in plant vacuoles.
• Raphides, a specific needle-like CaOx crystal morphology, have debated functions including calcium storage, heavy metal sequestration, and herbivore defense.
• The last comprehensive review of raphide distribution was published in 1980, necessitating an updated systematic review.

Purpose of the Study:

• To conduct an updated systematic review of the taxonomic and anatomical distribution of raphides in plants.
• To provide an overview of raphide-forming plant taxa and their phylogenetic distribution.
• To identify specific plant tissue locations where raphides are found.

Main Methods:

• A broad literature search was conducted to identify plant taxa and tissue locations containing raphides.
• Data on raphide occurrence was compiled and analyzed across different plant orders and families.
• Phylogenetic distribution at the order level and specific anatomical locations were reported.

Main Results:

• Raphide occurrence has been studied in 33 orders, 76 families, and 1305 species.
• Raphides were confirmed in 24 orders, 46 families, and 797 species, representing less than 1% of known species per family.
• Leaves were identified as the most common location for raphides across Eudicots, Magnoliids, and Monocots, while roots were least reported.

Conclusions:

• This review provides a foundational dataset for understanding the genetic origin and evolution of raphides in plants.
• The findings highlight specific plant groups and tissues for future research on raphide presence and function.
• Further studies are needed to fully elucidate the diverse roles of raphides in plant biology.