Just like in the animal kingdom, the plant kingdom has came up with some incredible weapons over the years. Offensive, and even defensive weapons have developed in plants to help them survive.
Poison Oak is about the best known of these plants, maybe due to the fact that if you ever got it, you never forget. "Leaves of three, let it be." Some of these plants have a way of planting in your mind forever the pain or discomfort you felt by picking it, eating it or even brushing up against it. I can see how this could help them survive. An animal might not want to mess with that one plant again, the one that made them welt up and itch in pain for days, or the one that poked them with a sharp thorn, in turn helping the plant survive.
Some plants have a defense to try and protect a fruit or flower. If you ever made your way with your hand through branches full of long sharp thorns to pick a lemon you will understand. They certainly make and leave a lasting impression, "leave me alone!"
Though not technically a plant, certain types of mushrooms are among the most deadly things possibly growing in your yard. Just look at some of the names of poisonous mushrooms. Death cap, Destroying angels, Devil's Bolete, poison pie and my favorite, "The Sickener", are but a few. Unless you are an expert, my best advice is to leave mushrooms alone. Buy them at the store. They are scary. Toad Stools are probably the most common we have in the Bay Area, and very deadly. I like to shovel them out of the yard on sight to protect people and pets, and but them in the green waste container. Never compost mushrooms.
There are lots of myths and wives tails about plants out there. One for example, is about Stinging Nettles, a common weed in the Bay Area. I once brushed against one in shorts while creek walking and had no idea what got me. It was horrible. A stinging pain shot up my legs into my whole body, I began to sweat and honestly felt like I was dying. This was long before the Internet and all this instant information. I asked others about it and learned, or so I thought, that it was the most poisonous plant in the world. I did not doubt that by my experience. So for years I was telling people to watch out,and how poisonous it was if eaten or even brushed up against. Stay away from it. It was not until recently that I read about it after finding it growing in our yard. I found out it is edible and they make tea and medicines out of it. It is also toxic, but only parts of it. I still leave it alone, but this is a great example of misinformation about plants.
This story is very similar to the myth tomatoes were poisonous. In fact the steams and roots are poisonous, but the fruit, as we finally found out, is very good. But be careful, in some cases it "is" all it's cracked up to be, like toad stools. And speaking of mushrooms again, there are lots of myths about mushrooms. One is the poison ones are brightly colored, and taste bad, both of which are not always true. So again, just leave the mushroom picking to the pro's. They are very scary.
I Think it is best to just assume all plants are poisonous if you do not know much about them. Who would think English Ivy, a popular house plant, is poisonous? Many pretty plants are poisonous, like Azaleas and Hydrangeas. Also plants that are used medicinally , like Aloe, Vera, are poisonous if used wrong. Some plants can be poisonous to our pets and not us. I read the Bird of Paradise is poisonous to dogs. And we all know about mistletoe, and how poisonous it is. Or is it? I guess I should read up on it, but again, I think it is best to just assume they are poisonous unless you know for sure. I won't be testing the Mistletoe question, that's for sure. Oleanders are probably the one plant with the most legend and stories written about it and it's use over the years to make poisons. It does seem to work to ward off gophers if you cut a few branches and stick them in a gopher hole. Maybe gophers know something, that just staying away is the best thing sometimes.
If you think about it, everything we have on earth comes from earth or space. So indeed natural does not automatically mean it is safe. You can find Cyanide, a popular poison, inside of Apple seeds and Cherry and Peach pits to name a few. Don't worry, you are safe if you accidentally swallow a cherry pit, but it just points out how something so natural can contain something so deadly. Maybe I should also read up more on that. Over time I have weeded out many myths from facts where plants are concerned, and you do learn something new everyday.
You can search the Internet for a list of common house plants that are poisonous for you or your pets. You may be surprised what is poisonous. Most animals have figured out, either by experience, taste, or even instinctually, what is poisonous and not. But with all these plants from other parts of the world in our houses, I would not take any chances. Life has to adapt over time to tolerate other forms of life and environments. When an animal or area is suddenly confronted with a new situation it has never seen before, the results can be disastrous.
Many plants and animals are not native to our area and become problems very quickly for our native species. Yellow Star thistle, a painful weed in it's own right, is one such weed. Poisonous to horses, it came from Asia most likely in contaminated horse feed sometime after the California Gold Rush, and quickly spread all over California. It is one of the plants I dread while weed eating. I had one shoot up and stick to my face once just under my safety glasses. Also having them stuck to my socks, they are an evil plant. Fox tails, a generic term for a weed with a fox tail sort of top to it, have some varieties native to Northern California, but I also dread those. Had one of those in my eye once, also from weed eating. They also can get stuck in dog's ears and are very hard to remove.
Over the years I have seen it all in the way of dangerous plants. Little cork screw weeds that can really get under your skin, to little Velcro type of weed seeds that stick all over you and cause irritation to your skin. Thorns of all types, some of which break off just under your skin and cause an infection. Of course Poison Oak, which I had seemed to have been immuned to for years, until one day, wham. I avoid that like the plague now. I've came across certain types of leaves that when dry and I rake them, I can't stop coughing for days.
I do not suffer from hay fever, but when you deal with the sheer amount of dust I do doing yard work, you will suffer eventually. Pollen, mold, you name it, there are countless types of plant hazards in your garden. Removal of some of these plants can be a bit tricky. Call a pro when in doubt. I like to spray poison oak from a safe distance and let it be. I will try to remove it if it is near my yard. Other types of dangerous plants require different approaches. As always, better safe than sorry. But please don't let a few thorns or a little poison oak keep you from enjoying the great outdoors. Best to just be aware of it , watch out and enjoy.
So now I am off to find some poison oak and other dangerous plants on the property to photograph for this article. And that is not exactly "leaving it be". I will be careful. Wear gloves and always wear eye protection when gardening. And always be aware of your surroundings, of both the good and bad things in nature. Because in the wisest of all sayings I have ever heard, and speaking words of wisdom, "if it's got leaves of three, let it be."