Green and red, classic Christmas colours, adorn the spiky holly shrub. A sprig may garnish puddings, but garnish nibblers like me must hold back on holly for it is poisonous in large doses - though some leaves can make a tasty beverage!
Holly includes about 400 species in the genus Ilex. The cultivated species is Ilex aquifolium, and about 20 or 30 of those bright berries can kill an adult.
Poisonings are more likely in pets or children, and about five berries will make a kid feel sick.
It's the usual suspects in symptoms - sleepiness, sore tummy, vomiting, diarrhoea. Larger doses cause paralysis, kidney damage and death.
Chemically, they contain a cocktail of active ingredients. Among them are the triterpenes, precursors to steroids which are cytotoxic (kill cells), steroids and a nitrile called menisdaurin.
Traditional medicines use holly for fever, gout and chronic bronchitis.
A couple of species native to North America, I. vomitoria aka yaupon and I. cassine, make caffeine and were used to make "black drink", a stimulating brew also used as a vomit-causing emetic.
South American species I. paraguariensis contains as much as 1.6% caffeine (five times more than the above species) and some of the cocoa chemical theobromine in their leaves, and tasty tannins.
Also called yerba mate, I. paraguariensis is brewed to make mate tea, which is delicious. It's pronounced MAH-tay, but be careful not to put the emphasis on the second syllable. Wikipedia says that makaes mah-TAY, which means "I killed" in Spanish.
So it's fine to have a sprig of holly in the house for Christmas, just don't make a holly pie out of it!