Calciimi oxalate crystals can be used to distinguish between different species. For example, butternut root bark contains only rosette crystals, while black walnut root bark — a common substitute — has both prisms and rosettes (Plate 78). These crystals are grouped into four principal classes: micro-crystals, raphides, rosettes, and solitary crystals.
Micro-crystals are the smallest of all the crystals. Under high power microscopy, they appear as V, Y, X, or T shapes (Plate 78) (Callout type="tip" title="Tip on Micro-Crystals"): They should be studied with the diaphragm nearly closed and the high-power objective in position.
Raphides resemble double-pointed needles. They are circular in cross-section, with the largest diameter at the center, tapering to sharp points (Plate 79) (Callout type="important" title="Important on Raphides"): Their presence or absence should always be noted when studying powders.
Rosette crystals are compound crystals composed of small crystals arranged in a radiating manner around a central core. They occur in frangula bark, spike-nard root, wahoo stem, and rhubarb (Plate 80) (Callout type="risk" title="Risk with Rosette Crystals"): The prisms forming rosette crystals decompose white light, often appearing variously colored.
Solitary crystals are the most variable. They usually occur in crystal cells associated with bast fibers and stone cells (Plate 82) (Callout type="beginner" title="Beginner on Solitary Crystals"): The more common forms include parallelopipeds and irregular polyhedrons, often longer than broad.
Cystoliths consist of calcium carbonate deposited over a framework of cellulose. They occur in special cavities or parenchyma cells (Plate 85) (Callout type="gear" title="Gear for Cystolith Identification"): When dilute hydrochloric acid is added, cystoliths produce a brisk effervescence with the evolution of carbon dioxide gas.
<Callout type="warning" title="Warning on Crystal Solubility">Crystals of calcium oxalate are freely soluble in dilute hydrochloric acid without effervescence; but they are insoluble in acetic acid and sodium and potassium hydroxide solutions.</Callout>
These crystals, for purposes of study, will be grouped into four principal classes, depending upon form and not upon crystal system. These classes are micro-crystals, raphides, rosettes, and solitary crystals.
CALCIUM OXALATE CRYSTALS IN SPECIFIC PLANTS Micro-crystals occur in belladonna, scopola, stramonium, and bittersweet leaves; in belladonna root, horse-nettle root, scopola rhizome, bittersweet stems, yellow and red cinchona bark, etc. (Plate 78) Raphides are usually seen in false unicorn root (Plate 79) and rarely as solitary crystals. Rosette crystals occur in frangula bark, spike-nard root, wahoo stem, root bark, rhubarb, etc. (Plate 80) Solitary crystals are the most variable of all the forms of calcium oxalate. They usually occur in crystal cells associated with bast fibers and stone cells.
CYSTOLITHS Cystoliths consist of calcium carbonate deposited over a framework of cellulose. They occur in special cavities, parenchyma cells (rubber-plant leaf, fig, pellionia), and non-glandular hairs (cannabis indica) (Plate 85).
TESTS FOR CYSTOLITHS When dilute hydrochloric acid or acetic acid is added to cystoliths a brisk effervescence takes place with the evolution of carbon dioxide gas.
PLATES AND FIGURES Plates 78, 79, 80, 82, 84, 85, and 86 illustrate various types of crystals in different medicinal plants. (Callout type="tip" title="Tip on Plate Usage"): Study these plates to identify the crystals accurately.
PLATE 78: Micro-Crystals
- Horse-nettle root (Solatium carolinense, L.), 2. Scopola rhizome (Scopola carniolica, Jacq.), 3. Belladonna root (Atropa belladonna, L.), 4. Bittersweet stem (Solanum didcamara, L.), 5. Scopola leaf (Scopola carniolica, Jacq.), 6. Tobacco leaf (Nicotiana tabacum, L.), 7. Belladonna leaf (Atropa belladonna, L.)
PLATE 79: Raphides
- Phytolacca n tima (L.) Baker), 2. Vallaria iCoraaJiaria nutjaiii, C), 3. Cartha^n ipecac {Cephttiii acuminata Karst.), 4. Bundle of raphides from false unicorn root. A. Bundle surrounded with mucilage. B. Mucilage expanded and partially dissolved. C. Bundle free of mucilage.
PLATE 80: Rosette Crystals
- Frangula bark (Rhamnus frangiUa, L.), 2. White oak bark {Qurrcus alba, L.), 3. Spikenard root (Aralia racemcsa, L.), 4. Wahoo etcm bark (Euonymus atropurptirau, Jact].), 5. Wahoo root bark (Euonymus atroptirpureui, Jacq.), 6. Rhubarb (Rheiim officinale, Balll.)
PLATE 82: Solitary Crystals
- Batavia cinnamon (cinnamomum burmanni, Nees), 2. Henbane leaves {Hyoscyamus niger, L.), 3. Morea nutgalls, 4. Codllana bark (Guarea rushyi [Brit ton], Rusby)
PLATE 84: Solitary Crystals
- G)ca leaf (Erythroxylon coca, Lamarck), 2. Xanthoxylum bark (Zanthoxylum americanum, Miller), 3. Elm bark (Ulmusfuiva, Michaux), 4. Spanish licorice root (Glycyrrhita glabra, L.), 5. White oak bark {Quercus alba^ L.)
PLATE 85: Solitary Crystals
- India senna (Cassia angustifolia, VahL), 2. Cascara sagrada bark {Rhamnus purshiana, D. C.), 3. Frangula bark (Rhamnus f ran gula, L.), 4. White pine bark (Pinus strohus, L.), 5. Tamarac bark (Larix laricina [Du Roi], Koch)
PLATE 86: Solitary Crystals
- Quassia {PicrtBna eoccelsa [Swartz.], Lindl.), 2. Uva-ursi leaf {Arctostaphyhs uva-ursi [L,], Spring.), 3. Quebracho bark {Aspidosperma quebracho'blanco, Schlechtendal), 4. Wild-cherry bark (Prunus seroHna, Ehrh.)
PLATE 87: Rosette Civstals and Solitary Crystals Occurring in
- Caacara sagrada bark (Rhamnus purshiana, D.C.), 2. Frangula bark (Riamnus frangula, L.), 3. Cundurango bark {Uarsdenia cundurango, [Trianal NicholB), 4. D<«wood root bark {Comus fiorida, L.), 5. Pleurisy root {Asdepias tvberosa, L.)
PLATE 88: Cystoliths in Ruellia Root and Cannabis Indica Hair
- Ruellia root (Ruellia ciliosa, Pursh.), 2. Pellionia leaf, 3. Cannabis indica (Cannabis saliva, variety Indica, Lam.)
Key Takeaways
- Identify different types of calcium oxalate crystals in medicinal plants.
- Use micro-crystals, raphides, rosettes, and solitary crystals for species differentiation.
- Understand the solubility tests for cystoliths.
Practical Tips
- Always use a high-power objective when studying micro-crystals to observe their structure more clearly.
- Note the presence or absence of raphides in powders as it can be critical for identification.
- Study plates and figures carefully to accurately identify crystals in different medicinal plants.
Warnings & Risks
- Be cautious with raphides, as they are sharp-pointed and can cause injury if mishandled.
- Solitary crystals are highly variable, so always check multiple samples when identifying them.
- Cystoliths require specific tests for identification; failure to perform these tests could lead to misidentification.
Modern Application
The techniques described in this chapter on identifying calcium oxalate crystals remain relevant today. While modern methods have advanced, the fundamental knowledge of crystal morphology and solubility tests still applies. This information is crucial for triage emergency response, where quick and accurate identification can be life-saving.
Frequently Asked Questions
Q: How do you identify micro-crystals in medicinal plants?
Micro-crystals are identified under high power microscopy as V, Y, X, or T shapes. They should be studied with the diaphragm nearly closed and the high-power objective in position.
Q: What is a raphide crystal and how can it be recognized?
Raphides resemble double-pointed needles. They are circular in cross-section, with the largest diameter at the center, tapering to sharp points. Their presence or absence should always be noted when studying powders.
Q: What are the different types of calcium oxalate crystals mentioned in this chapter?
The chapter mentions four principal classes: micro-crystals, raphides, rosettes, and solitary crystals. Each type has distinct characteristics that can be used for identification.