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Raphide

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Raphides in Epipremnum Devil's ivy (600x magnification)
Raphides in Epipremnum Devil's ivy (600x magnification)

Raphides (/ˈræfɪdiz/ RAF-id-eez; singular raphide /ˈrfd/ RAY-fyde or raphis) are needle-shaped crystals of calcium oxalate monohydrate (prismatic monoclinic crystals) or calcium carbonate as aragonite (dipyramidal orthorhombic crystals), found in more than 200 families of plants. Both ends are needle-like, but raphides tend to be blunt at one end and sharp at the other.

Calcium oxalate in plants

Raphides in Hypoestes phyllostachya, the polka dot plant
Raphides in Hypoestes phyllostachya, the polka dot plant

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.

Discover more about Calcium oxalate in plants related topics

Hypoestes phyllostachya

Hypoestes phyllostachya

Hypoestes phyllostachya, the polka dot plant, is a species of flowering plant in the family Acanthaceae, native to South Africa, Madagascar, and south east Asia. The spots often merge into larger areas of colour.

Parenchyma

Parenchyma

Parenchyma is the bulk of functional substance in an animal organ or structure such as a tumour. In zoology it is the name for the tissue that fills the interior of flatworms.

Idioblast

Idioblast

An idioblast is an isolated plant cell that differs from neighboring tissues. They have various functions such as storage of reserves, excretory materials, pigments, and minerals. They could contain oil, latex, gum, resin, tannin or pigments etc. Some can contain mineral crystals such as acrid tasting and poisonous calcium oxalate or carbonate or silica. Any of the tissue or tissue systems of plants can contain idioblasts. Idioblasts are divided into three main categories: excretory, tracheoid, and sclerenchymatous.

Agave americana

Agave americana

Agave americana, common names century plant, maguey, or American aloe, is a species of flowering plant in the family Asparagaceae, native to Mexico and the United States in Texas. It is cultivated worldwide as an ornamental plant, and has been naturalized in many regions, including parts of the West Indies, South America, Mediterranean Basin, Africa, Canary Islands, India, China, Thailand, and Australia.

Tradescantia pallida

Tradescantia pallida

Tradescantia pallida is a species of spiderwort similar to T. fluminensis and T. zebrina. The cultivar T. pallida 'Purpurea' is commonly called purple secretia, purple-heart, or purple queen. It is native to the Gulf Coast region of eastern Mexico. Edward Palmer collected the type specimen near Ciudad Victoria, Tamaulipas in 1907.

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 predators,[7] as they are likely to tear and harm the soft tissues of the throat or esophagus of a plant predator 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 Indian turnip which contain large quantities of raphides, the roots are not unpalatable when cooked because the raphides are bound within a matrix of starch which prevents the tongue from sensing their presence. Some other plants store raphides in mucilaginous environments and also do not taste acrid.[3]

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.

Actinidiaceae:

Amaranthaceae:

Araceae:

Araliaceae:

Arecaceae:

Asparagaceae:

Bromeliaceae:

Commelinaceae:

Onagraceae:

Polygonaceae:

Rubiaceae:

Vitaceae:

Discover more about Plants containing raphides related topics

Araceae

Araceae

The Araceae are a family of monocotyledonous flowering plants in which flowers are borne on a type of inflorescence called a spadix. The spadix is usually accompanied by, and sometimes partially enclosed in, a spathe. Also known as the arum family, members are often colloquially known as aroids. This family of 140 genera and about 4,075 known species is most diverse in the New World tropics, although also distributed in the Old World tropics and northern temperate regions.

Commelinaceae

Commelinaceae

Commelinaceae is a family of flowering plants. In less formal contexts, the group is referred to as the dayflower family or spiderwort family. It is one of five families in the order Commelinales and by far the largest of these with about 731 known species in 41 genera. Well known genera include Commelina (dayflowers) and Tradescantia (spiderworts). The family is diverse in both the Old World tropics and the New World tropics, with some genera present in both. The variation in morphology, especially that of the flower and inflorescence, is considered to be exceptionally high amongst the angiosperms.

Actinidiaceae

Actinidiaceae

The Actinidiaceae are a small family of flowering plants. The family has three genera and about 360 species and is a member of the order Ericales.

Actinidia

Actinidia

Actinidia is a genus of woody and, with a few exceptions, dioecious plants native to temperate eastern Asia, occurring throughout most of China, Taiwan, Korea, and Japan, and extending north to southern areas of Russian Far East and south into Indochina. The genus includes shrubs growing to 6 metres tall, and vigorous, strong-growing vines, growing up to 30 m (100 ft) in tree canopies. They mostly tolerate temperatures down to around −15 °C (5 °F), and some are much hardier.

Amaranthaceae

Amaranthaceae

Amaranthaceae is a family of flowering plants commonly known as the amaranth family, in reference to its type genus Amaranthus. It includes the former goosefoot family Chenopodiaceae and contains about 165 genera and 2,040 species, making it the most species-rich lineage within its parent order, Caryophyllales.

Beta (plant)

Beta (plant)

Beta is a genus in the flowering plant family Amaranthaceae. The best known member is the common beet, Beta vulgaris, but several other species are recognised. Almost all have common names containing the word "beet". Wild Beta species can be found throughout the Atlantic coast of Europe, the Mediterranean coastline, the Near East, and parts of Asia including India.

Alocasia

Alocasia

Alocasia is a genus of rhizomatous or tuberous, broad-leaved, perennial, flowering plants from the family Araceae. There are about 90 accepted species native to tropical and subtropical Asia and eastern Australia. Around the world, many growers widely cultivate a range of hybrids and cultivars as ornamentals.

Arisaema

Arisaema

Arisaema is a large and diverse genus of the flowering plant family Araceae. The largest concentration of species is in China and Japan, with other species native to other parts of southern Asia as well as eastern and central Africa, Mexico and eastern North America. Asiatic species are often called cobra lilies, while western species are often called jack-in-the-pulpit; both names refer to the distinctive appearance of the flower, which consists of an erect central spadix rising from a spathe.

Arum

Arum

Arum is a genus of flowering plants in the family Araceae, native to Europe, northern Africa, and western and central Asia, with the highest species diversity in the Mediterranean region. Frequently called arum lilies, they are not closely related to the true lilies Lilium. Plants in closely related Zantedeschia are also called "arum lilies".

Caladium

Caladium

Caladium is a genus of flowering plants in the family Araceae. They are often known by the common name elephant ear, heart of Jesus, and angel wings. There are over 1000 named cultivars of Caladium bicolor from the original South American plant.

Colocasia

Colocasia

Colocasia is a genus of flowering plants in the family Araceae, native to southeastern Asia and the Indian subcontinent. Some species are widely cultivated and naturalized in other tropical and subtropical regions.

Araliaceae

Araliaceae

The Araliaceae are a family of flowering plants composed of about 43 genera and around 1500 species consisting of primarily woody plants and some herbaceous plants. The morphology of Araliaceae varies widely, but it is predominantly distinguishable based on its woody habit, tropical distribution, and the presence of simple umbels.

Source: "Raphide", Wikipedia, Wikimedia Foundation, (2023, January 25th), https://en.wikipedia.org/wiki/Raphide.

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References
  1. ^ Webb, M. A. (1999). "Cell-Mediated Crystallization of Calcium Oxalate in Plants". The Plant Cell Online. 11 (4): 751–761. doi:10.1105/tpc.11.4.751. PMC 144206. PMID 10213791.
  2. ^ Horner Jr, H. T.; Whitmoyer, R. E. (1972). "Raphide crystal cell development in leaves of Psychotria punctata (Rubiaceae)" (PDF). Journal of Cell Science. 11 (2): 339–55. doi:10.1242/jcs.11.2.339. PMID 4342516.
  3. ^ a b Weber, R. A. (1891). "Raphides, the Cause of the Acridity of Certain Plants". Journal of the American Chemical Society. 13 (7): 215–217. doi:10.1021/ja02124a034. Also, doi:10.1038/scientificamerican11211891-13242csupp
  4. ^ Wattendorff, Joachim (1976). "A third type of raphide crystal in the plant kingdom: Six-sided raphides with laminated sheaths in Agave americana L". Planta. 130 (3): 303–11. doi:10.1007/BF00387837. PMID 24424644. S2CID 22882070.
  5. ^ According to this abstract in the FDA Poisonous Plant Database Agave americana contains calcium oxalate crystals, acrid oils, saponins, and other compounds.
  6. ^ Wu, H; Zhong, L. Y. (2008). "Study on irritation of calcium oxalate crystal in Araceae plants". Zhongguo Zhong Yao Za Zhi (in Chinese). 33 (4): 380–4. PMID 18533491.
  7. ^ Arnott, H. J.; Webb, M. A. (2000). "Twinned Raphides of Calcium Oxalate in Grape (Vitis): Implications for Crystal Stability and Function". International Journal of Plant Sciences. 161 (1): 133–142. doi:10.1086/314230. JSTOR 3080127. PMID 10648203. S2CID 3009411.
  8. ^ "Animal Poison Control Center: Taro". ASPCA.
  9. ^ "Plant poisoning -- Calcium oxalate crystals". Right Diagnosis from Healthgrades.
  10. ^ Watson, John T.; Jones, Roderick C.; Siston, Alicia M.; Diaz, Pamela S.; Gerber, Susan I.; Crowe, John B.; Satzger, R. Duane (2005). "Outbreak of Food-borne Illness Associated with Plant Material Containing Raphides". Clinical Toxicology. 43 (1): 17–21. doi:10.1081/CLT-44721. PMID 15732442. S2CID 388923.

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