Raphide
Raphides (
Calcium oxalate in plants
Many plants accumulate calcium oxalate crystals in response to surplus calcium, which is found throughout the natural environment. The crystals are produced in a variety of shapes. The crystal morphology depends on the taxonomic group of the plant. In one study of over 100 species, it was found that calcium oxalate accounted for 6.3% of plant dry weight.[1] Crystal morphology and the distribution of raphides (in roots or leaves or tubers etc.) is similar in some taxa but different in others leaving possible opportunities for plant key characteristics and systematic identification; mucilage in raphide containing cells makes light microscopy difficult, though. Little is known about the mechanisms of sequestration or indeed the reason for accumulation of raphides but it is most likely as a defense mechanism against herbivory. It has also been suggested that in some cases raphides may help form plant skeletal structure. Raphides typically occur in parenchyma cells in aerial organs especially the leaves, and are generally confined to the mesophyll. As the leaf area increases, so does the number of raphides, the process starting in even young leaves. The first indications that the cell will contain crystals is shown when the cells enlarge with a larger nucleus.[2]
Raphides are found in specialized plant cells or crystal chambers called idioblasts.[3] Electron micrographs have shown that raphide needle crystals are normally four sided or H-shaped (with a groove down both sides) or with a hexagonal cross section and some are barbed. Wattendorf (1976) suggested that all circular sectioned raphides, as visible in a light microscope, are probably hexagonal in cross section[4] The hexagonal crystals reported by Wattendorf in Agave americana were apparently calcium oxalate.[5]
Microscopy using polarized light shows bright opalescence with raphides.
Plants like Tradescantia pallida also accumulate calcium oxalate crystals in response to heavy metals stress.[citation needed]
Harmful effects
Raphides can produce severe toxic reactions by facilitating the passage of toxin through the herbivore's skin when the tissue containing the raphides also contains toxins. The lethal dose to mice is around 15 mg/kg.[6] Raphides seem to be a defense mechanism against plant consuming animals,[7] as they are likely to tear and harm the soft tissues of the throat or esophagus of an animal chewing on the plant's leaves.[8][9] The venomous process is in two stages: mechanical pricking and injection of harmful protease. Typically ingestion of plants containing raphides, like those common in certain houseplants, can cause immediate numbing followed shortly by painful edema, vesicle formation and dysphagia accompanied by painful stinging and burning to the mouth and throat with symptoms occurring for up to two weeks.[10] Airway assessment and management are of the highest priority, as are extensive irrigation and analgesics in eye exposure.
Raphides cannot normally be destroyed by boiling; that requires an acidic environment or chemical solvents like ether. Plants containing large amounts of raphides are generally acrid and unpalatable. However, it is not always possible to detect the presence of raphides through taste alone. In some tubers such as
Plants containing raphides
Common names vary. The following list is incomplete. Raphides are found in many species in the families Araceae and Commelinaceae, but are also found in a few species in a number of other families.
- Actinidia (Kiwifruit)
- Alocasia (Baibing in NE India)
- Arisaema (Cobra Lily)
- Arum (Cuckoopint)
- Caladium (Angel wings)
- Colocasia (Taro, Cocoyam, Eddoe)
- Dieffenbachia (Dumb Cane)
- Epipremnum (Devil's Ivy, Golden Pothos)
- Monstera (Swiss Cheese Plant)
- Philodendron (Elephant Ears)
- Spathiphyllum (Peace Lily)
- Zantedeschia (Calla Lily)
- Brassaia(Umbrella Tree)
- Caryota (Fishtail Palm)
- Ptychosperma
- Arenga
- Hyophorbe verschaffeltii (Spindle palm)
- Agave (Agave)
- Chlorophytum orchidastrum (Green Orange)
- Ananas comosus(Pineapple)
Commelinaceae:
- Commelina (Dayflower)
- Tradescantia (Wandering Jew)
- Triceratella
- Fuchsia (Fuchsia)
- Cenchrus echinatus (sandbur)
- Rheum rhabarbarum (Rhubarb)
- Parthenocissus quinquefolia (Virginia creeper)
See also
References
- PMID 10213791.
- PMID 4342516.
- ^
- S2CID 22882070.
- ^ According to this abstract in the FDA Poisonous Plant Database Agave americana contains calcium oxalate crystals, acrid oils, saponins, and other compounds.
- PMID 18533491.
- S2CID 3009411.
- ^ "Animal Poison Control Center: Taro". ASPCA.
- ^ "Plant poisoning -- Calcium oxalate crystals". Right Diagnosis from Healthgrades.
- S2CID 388923.