POISONOUS PLANTS

Many plants are grown each year, both in the house and the garden, that are poisonous to varying degrees. The numbers are truly staggering and only a few can be listed here

What is a poisonous plant? Poisonous plants broadly include members of the cyanobacteria (blue-green algae), fungi, ferns, cone-bearing and flowering plants. They are understood by most people to be those which cause illness, or death, in humans or domestic animals after being eaten. Whether a plant is poisonous or not depends on the capacity of the animal eating it to cope with the chemicals it contains. The outcome of eating such plants may be further complicated if the concentration of their toxins varies with the stage of growth of the plants or the seasonal conditions, rendering the plant more hazardous at some times than at others. What do poisonous plants look like? There are thousands of plants that are toxic, some more than others, and there are no common characteristics of form, colouring, odour or taste which distinguish a poisonous plant from a non-poisonous plant. To avoid poisoning, we need to learn what the known poisonous plants look like, based on the knowledge generated by past experience and scientific studies of the subject.
Why are plants poisonous? Current opinion appears to be that many of the plant chemicals toxic to humans and livestock are produced as part of the plant's defences against being eaten or to gain an advantage over competing plants. Many of these defences are directed against insects. This makes the poisoning of people and their animals truly "accidental" and "collateral damage" in the long wars between plant and plant and between plants and the insects which eat them.