One of the more common toxins, insoluble calcium oxalate crystals can be found in many popular houseplants and ornamentals. The vast majority of these plants belong to the Araceae family and all cause a similar clinical syndrome. Within the Aracae, genera such as Alocasia, Arisaema, Caladium, Colocasia, Dieffenbachia and Philodendron contain calcium oxalate crystals in the form of raphides. The Araceae family is one of the most diverse in the plant kingdom, comprising over 3700 different species. When consumed, these plants cause an intense burning sensation of the mouth, throat, lips and tongue; excessive drooling, choking, gagging and potentially serious swelling of the throat that could cause difficulty or the inability to swallow (dysphagia). Symptoms can occur immediately or up to 2 hours after ingestion and may continue to occur for up to two weeks after ingestion.

All parts of these plants should be considered toxic, although the leaves of some species may contain little or no toxin. These plants contain special cells called idioblasts. Found in a number of plant species both poisonous and non-poisonous, idioblasts differ from neighboring cells in that they contain non-living substances like oil, latex, gum, resin, tannin, pigments or minerals. One of these substances is raphides or bundles of needlelike crystals of calcium oxalate that tend to be blunt at one end and sharp at the other. The crystals are packed in a gelatinous substance that contains free oxalic acid.

When animals chew on the leaves, flowers or stems of the plant, the tip of the idioblast is broken allowing saliva from the animal or sap from the plant to enter the cell. This in turn causes the gelatinous material to swell forcing the raphides (needle like calcium oxalate crystals) to violently shoot out from the cells into the surrounding area. The calcium oxalate crystals then penetrate and embed themselves into the tissues of the mouth, tongue, throat and stomach causing (in most cases) immediate discomfort and aggravation as would be expected when millions of microscopic needles are lodged in ones throat and mouth. The idioblasts may continue to expel raphides for a considerable amount of time after ingestion allowing the crystals to also embed themselves into lining of the stomach and intestine causing additional gastrointestinal upset.

In addition to calcium oxalate crystals some species may also contain proteinase (proteolytic enzymes) that break protein down into amino acids stimulating the release of kinins and histamines; which cause inflammation, affect blood pressure and stimulate pain receptors. Although kinins and histamines are part of the body’s natural response to tissue damage and foreign bodies, the inflammatory response will only serve to exacerbate the damage and irritation caused by the embedded calcium oxalate crystals.

In the vast majority of cases clinical signs will present immediately or within two hours of ingestion. Clinical signs include obvious pain and irritation that is generally expressed by violently shaking the head, drooling excessively, pawing at the mouth, gagging, vomiting or dry heaving. The animal may also whine, bark or yelp in an unusually hoarse or weak sounding voice. Other clinical signs include depression, diarrhea, inappetance and swelling of the mouth, throat and tongue. In some cases swelling may be so severe as to restrict oxygen intake resulting in dyspnea (shortness of breath, gasping for air). The crystals irritation of the stomach also commonly results in diarrhea.

Due to the fact that the plant is both bitter in taste and acts as an immediate irritant to the mouth, large ingestions are uncommon. If, however, a pet does manage to tolerate consuming a massive amount the plant clinical signs will be notably worse. So much so, that the vomiting and diarrhea can severely dehydrate the animal, cause electrolyte imbalances and send the animal into shock. In cases involving massive ingestions; cardiac abnormalities, dilated pupils, coma and death have been reported.