Begonia

The begonia is a genus of perennial flowering plants in the family Begoniaceae. Begonia is the sixth largest flowering plant genus and contains over 1,500 species and some 10,000+ hybrids. As there are so many species it is impossible to provide an accurate one size fits all description. In general the majority of begonia species are terrestrial (grow in the earth); some are known to grow from other plants such as trees (epiphytic). The plants are typically considered herbs or undershrubs and are native to the subtropical and tropical moist climates of South and Central America, Africa and southern Asia. In the wild terrestrial species are commonly upright-stemmed, rhizomatous, or tuberous. In most species the fruit is a winged capsule containing numerous minute seeds, although berry type fruits are also known. The leaves, which are often large and variously marked or variegated, are usually asymmetric (unequal-sided).

There are two potentially toxic agents in the tuberous portion of begonias, calcium oxalates and cucurbitacin B. The first, calcium oxalate crystals are one of the more common plant toxins and can be found in hundreds of popular houseplants and ornamentals. 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.

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 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.

The second toxic compound “cucurbitacin B” is a biochemical compound produced by the plant in order to defend itself from being eaten. Cucurbitacins are generally cytotoxic (promote cell death) and can be extremely poisonous to some animal species. Additionally, cucurbitacins are also known for providing plants with an extremely bitter and displeasing taste.

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. Additionally, the toxins are located in the underground portions (tubers) of the plant and the toxin amount is relatively low, so potentially life-threatening or serious intoxication of a pet from begonia (while theoretically possible) is basically unheard of. It may be that like the tomato, the potential danger posed by begonia has been blown a bit out of proportion. In regards to the plants toxicity towards humans, the University of Nebraska Cooperative Extension in Lancaster County lists begona as non-toxic, with the notation “that these plants have shown no more toxicity than an equal amount of vegetable matter. Symptoms are unlikely”.