RHUBARB (RHEUM RHABARBARUM)
The large, coarse leaves of rhubarb are anxiously awaited by many Nova Scotians in early spring. This plant provides fleshy, sour stalks, superb in pies and in fruit mixtures with strawberries.
It owes its flavour, in part, to the presence of oxalate crystals. These needle-like irritants are the primary reason for not grazing the leaves, neither child nor pet.
In addition, various glycosides may be responsible for symptoms of poisoning.
Leaves of the plant, although other parts may also contain the toxin.
Docks and sorrels contain oxalate crystals, which give them a characteristic sour taste, resembling rhubarb, another relative.
Members of the buckwheat family, including buckwheat and some knotweed species, are also said to have the property of causing photosensitivity of the skin, although one would have to consume a large volume or be hypersensitive.
Rhubarb leaves may also contain glycosides.
TYPICAL POISONING SCENARIO
Livestock can be affected by excessive grazing of the leaves of dock and rhubarb. Additionally, if humans eat dock and sorrel leaves as potherbs to excess, calcium absorption may be impeded. Accidental ingestion of rhubarb leaves by children is also problematic.
"In mild cases, overindulgence in dock and sorrel can lead to severe abdominal pain, nausea, vomiting, burning of the mouth and throat, and muscular twitching. Large amounts may be lethal or, at the very least, cause permanent liver and kidney damage.
In photosensitivity, skin rashes, itching, redness, and/or ulceration develop after exposure to direct sunlight. Ultimately, the dermatitis can lead to a secondary infection from scratching, which may scar the skin or become a systemic infection.
RHUBARB POISON INFORMATION
Glycosides are toxins in which at least one sugar molecule is linked with oxygen to another compound, often nitrogen-based. They become harmful when the sugar molecule is stripped off, as in the process of digestion.
Oxalates are unstable salts of oxalic acid. When eaten, they break down to release the highly poisonous acid.
The sour flavour of sorrel (Rumex species), wood sorrel (Oxalis), and even rhubarb is due to the presence of the acid.
Some plants may contain differing amounts of potassium or calcium salts, rendering them unsafe, particularly in the buckwheat and goosefoot families.