As part of their natural defense mechanism, many plants contain alkaloids and glycosides.
Although you won't find most of these at your garden center, it's still good to know
your enemies in the naturalscape.
What's interesting to note is how many of our agricultural crops carry potentially
toxic poisons. Look at Rheum x cultorum (common rhubarb) which contains soluble oxalates
and anthraquinone glycosides in the leaves that causes all sorts of problems if taken internally,
even small amounts.
And of course there's the opposite story about those bright red berries brought back from
the new world that nobody would dare to eat -- Solanum lycopersicum, our very safe and
very edible garden tomato. (In fact, some members of the Solanum genus [nightshades]
do contain a steroidal glyco-alkaloid which causes solanine poisoning.)
Index to potentially poisonous plants
Pacific poison oak
This climbing ivy sports leaves with a variety of forms
making it difficult to spot with certainty. But every autumn the leaves turn bright
red making it a dead give-away.