**6. Plant families and the types of ergastic crystals in plants**

The distribution and characterization of ergastic crystals indicate that they are unique entities in the circumscription and delimitation of various taxa. A review of the calcium oxalate crystals in plants is presented in detail [30]. Calcium oxalate crystals are widely distributed and enlisted in 215 plant families [38]. Systematic significance of the formation, occurrence and distribution of crystals were studied in leaves of 22 species of *Combretum* [39]. Studies on anther anatomy of 167 species of Fabaceae plant family and wood anatomy of 139 species of Verbenaceae plant family reported several types of crystals [40, 41]. The wood anatomy of the plant family Lauraceae revealed the presence of significant prismatic crystals while the plant family Tiliaceae shows the presence of conglomerate crystals [42].

Christina reviewed the structure and systematics of calcium crystals in monocotyledons especially their occurrence of these crystal types, with respect to current systematics [43]. The three main types of calcium oxalate crystal that occur in monocotyledons are raphides, styloids and druses, although intermediates are sometimes recorded. It is inferred that the presence or absence of the different crystal types may represent 'useful' taxonomic characters. Further, styloids are characteristic of some families of Asparagales, notably Iridaceae, where raphides are entirely absent. Raphides are predominant in Monocots mainly seen in leaf petiole of Araceae [42, 44] Styloids are seen in Agavaceae [45]. In *Dracaena sanderiana* (Liliaceae) two types of intracellular calcium oxalate deposits are reported: calcium oxalate monohydrate raphides and solitary calcium oxalate dihydrate crystals [46]. Archeological significance of raphides in Araceae is studied by [6].

zinc [20]. Oxalic acid is also reported to help in the accumulation of heavy metals, cadmium, nickel, zinc, etc. by hyper- accumulators that are being utilized in phytoremediation of soils

Of the five types of calcium oxalate crystals, raphides are prominent ones in terms of size and quantity as it can occur intercellular and intracellular. Calcium oxalates gets incorporated in human body through plant-based food. These along with the endogenously synthesized content contribute to kidney problems. Studies reveal that calcium oxalates are present in algae, fungi and lichens in addition to their presence in higher plants. Out of all the three forms of calcium oxalate, the monohydrate form is the one widely reported to cause kidney problems [24]. Calcium oxalate, a potential causative agent of human kidney stones, can range from 3 to 80% of the dry weight of various plants [25, 26] and it can contribute up to 70 or 75% of the composition of kidney stones [27]. Deleterious influence of raphides includes promoting kidney stone formation, irritation to throat, mouth and skin [28–32]. Excess presence of raphides, in conjugation with cytotoxic compounds [5, 33], can render the food poisonous and is respon-

Crystallized calcium oxalates that appear, as bundles of needles under light microscopes are usually raphides [28, 36]. It is believed that herbivory enhances raphide production in plant cells and the coexisting cysteine proteases together with other defensive chemicals promote protection against grazing animals. The needle like raphides cause bruising the alimentary tract lining of herbivores and also causes irritation due to presence of cysteine proteases [31]. The additive effect of irritants such as cysteine proteases and raphides has been proved in

The distribution and characterization of ergastic crystals indicate that they are unique entities in the circumscription and delimitation of various taxa. A review of the calcium oxalate crystals in plants is presented in detail [30]. Calcium oxalate crystals are widely distributed and enlisted in 215 plant families [38]. Systematic significance of the formation, occurrence and distribution of crystals were studied in leaves of 22 species of *Combretum* [39]. Studies on anther anatomy of 167 species of Fabaceae plant family and wood anatomy of 139 species of Verbenaceae plant family reported several types of crystals [40, 41]. The wood anatomy of the plant family Lauraceae revealed the presence of significant prismatic crystals while the plant

Christina reviewed the structure and systematics of calcium crystals in monocotyledons especially their occurrence of these crystal types, with respect to current systematics [43]. The three main types of calcium oxalate crystal that occur in monocotyledons are raphides, styloids and druses, although intermediates are sometimes recorded. It is inferred that the presence or absence of the different crystal types may represent 'useful' taxonomic characters. Further, styloids are characteristic of some families of Asparagales, notably Iridaceae, where

**6. Plant families and the types of ergastic crystals in plants**

family Tiliaceae shows the presence of conglomerate crystals [42].

affected by toxicity of these heavy metals [21–23].

34 Herbal Medicine

sible for mentionable fatalities every year [34, 35].

larvae and caterpillar [37].

In Gymnosperms, druses, prismatic crystals and solitary crystals are observed. Druses are seen in the leaf vascular tissue of *Ginkgo biloba* [47]. In Pinaceae, wood CaOx ray cells and cork of stem contain solitary and prismatic crystals. Calcium oxalate crystals are considered to enhance internal source of carbon dioxide in plants [48]. This is recorded in *Amaranthus hybridus (Amaranthaceae), Dianthus chinensis (Caryophyllaceae), Pelargonium peltatum (Gesneriaceae)* and *Portulacaria afra (Portulacaceae)*. Occurrence, type and location of calcium oxalate crystals have been investigated in *Achyranthes aspera (*Amaranthaceae), *Adhatoda zeylanica (*Acanthaceae), *Aerva lanata* (Amaranthaceae), *Asparagus racemosus* (Asparagaceae), *Atalantia monophylla* (Rutaceae). *Bridelia crenulata* (Euphorbiaceae) *Carica papaya* (Caricaceae) *Carissa spinarum* (Apocynaceae), *Plumeria rubra* (Apocynaceae) *Monochoria vaginalis* (Pontederiaceae) [49].

The types and distribution of calcium oxalate crystals in leaves and stems of some species of poisonous plants have been studied. Crystal sands and prismatic crystals were of rare occurrences. Prismatic crystals were observed in the leaf mesophyll cells of *Nerium oleander* and *Cynanchum acutum*. It was concluded that there is no absolute correlation between the presence and type of calcium oxalate crystals and toxic plant organs.

An extensive enumeration of calcium oxalate crystal reports has been done [28] in 215 plant families including genus *Sida* of Malvaceae. Further, the relation between herbivory and calcium concentration has been recorded in the leaves of *Sida* species. Cell mediated crystallization of calcium oxalate is reported by Webb [25]. The structures of cystoliths in selected taxa of the genus Ficus L. (Moraceae) in the Malaysia Peninsular have been investigated [50]. The characteristics of the cystoliths may not suitably be used as a taxonomic marker but it can be useful as additional character for group identification in *Ficu*s.

New and unusual forms of calcium oxalate raphide crystals in the plant kingdom [51] from the tubers of *Dioscorea polystachya*—six-sided needles with pointed ends and four-sided needles with beveled ends. The production of calcium oxalate crystals has a long evolutionary history and probably evolved independently in major clades of symbiotic fungi and several times in the plantae, as part of the overall process of bio-mineralization [29].
