Over 400,000 species of plants exist today. An unknown number of species, perhaps several hundred thousand, existed at one time but are now extinct. Virtually all this diversity came about through evolution by natural selection—survival of the fittest. Because organisms are exposed to various adverse conditions, those individuals best-fit (adapted) to a particular environment are more likely to survive. For any particular aspect of the environment many adaptations are possible. Plants have developed physical and chemical defense mechanisms to cope with adverse environmental conditions. Consider plants growing in freezing winters; frozen soil is physiologically dry because roots cannot extract water from it. They survive because mutations have occurred that cause their leaves to drop in the fall. They also have bark on the stems that reduces the amount of water lost through their stems. Desert plants conserve water in different ways: they are smaller with fewer leaves and have thick waxy cuticles. Another adaption is seen in the aster family (sunflowers, daisies) which produce a group of chemical compounds that discourage herbivores. Other plant adaptions include leaf modifications like thorns, spines, and barbs.

Plant defense mechanisms can have adverse effects on people. It is never a good idea to pick or disturb plants you are unfamiliar with! The following is a list of plant tips to consider when you are dealing with plants:

1. Know the poisonous plants in your house or garden

2. Do not put any plant or plant part in your mouth unless you know for sure it is not poisonous.

3. Don't eat unfamiliar berries; they may be OK for birds but not for us.

4. Don't eat any wild mushrooms.

5. Do not touch plants that have milky secretions.

6. Don't burn unfamiliar sticks; especially for marshmallows or hotdogs.

7. Don't leave dangerous plants near young children or pets.

8. Call the Poison Control Center if you suspect someone has eaten a poisonous plant.

9. Call 911, the police, or an ambulance for emergencies.

10. Stay calm! Most poisonous plants cause a mild reaction and have a cure.