People associate cities with traffic, asphalt, and buildings. San Francisco often seems like one enormous parking lot: disconnected from nature. But there’s a real jungle coexisting with the urban jungle. Hiding in plain sight are an abundance of deadly plants. These range from the terrifying — like the deliriant Brugmansia aurea — to the lethal: Ricinus communis. I spent a day walking around San Francisco identifying some of the deadly plants that live among us. None of these plants are in inaccessible areas: all are easily spotted from streets or parks. Anyone can identify, observe, and maybe even bring home some of these poisonous plants.

1. American Black Nightshade

Solanum americanum

South-West corner of Geary and Webster

The Solanum genus contains many edible plants like tomatoes, potatoes, and eggplants. But it also contains several poisonous species. The fruits of the American Black Nightshade contain the glycoalkaloids solanine and solamargine. Consumption can cause nausea, vomiting, cardiac dysrhythmia, paralysis, and death. Children have died from eating unripe berries, which are especially toxic.

Early European colonists in the Americas avoided consuming tomatoes because of their association with the nightshade family: American Black Nightshade strongly resembles a tomato plant. Confusing the two can have disastrous results — in fact, there were tomatoes growing less than 10 meters from where I identified nightshade in Japantown.

This plant is especially sinister because of its appealing fruits and widespread distribution. Among all the plants on this list, American Black Nightshade is probably the easiest to accidentally consume.

2. Poison Hemlock

Conium maculatum

Stanyan and Kezar

While I was walking from Haight-Ashbury to Golden Gate Park I came across a tall, withered plant with prominent floral corymbs that resemble those of a wild carrot and pinnated leaves that look like parsley. This plant is poison hemlock.

Poison hemlock native to the Mediterranean and traveled to the Americas along with European colonists. Hemlock contains high levels of the alkaloids coniine and coniceine. These alkaloids attack the central nervous system, suppressing the respiratory muscles and leading to vasoconstriction — especially in the lower body (more on that below) — and death.

A brew of hemlock is infamous for being the plant that killed the philosopher Socrates. His reaction to the poison was typical: “the attendant examined Socrates’ feet and legs, then the man pinched his foot hard and asked if he felt it. Socrates said “No”; then after that, his thighs; and passing upwards in this way he showed us that he was growing cold and rigid. And then again he touched Socrates and said that when it reached his heart, he would be gone. The chill had now reached the region about the groin, and uncovering his face the attendant saw that Socrates’ eyes were fixed.”

3. White Snakeroot

Ageratina altissima

Lily Pond, Golden Gate Park

White snakeroot contains tremetol, which is named after the “trembles” caused by ingesting the poison. While it’s extremely uncommon to be poisoned by white snakeroot today, there was a time when milk sickness —caused by drinking milk produced by cows that had eaten snakeroot — killed thousands of American settlers in the Midwest. Nancy Lincoln — the mother of Abraham Lincoln — died of milk sickness.

Although white snakeroot is not as dangerous as the previous two entries in this list, it deserves a place here because of the historical damage it caused. More people have likely died of snakeroot poisoning than all the other poisonous plants on this list combined.

4. Angel’s Trumpets

Brugmansia aurea

520 Oak Street

The alluring trumpets of the brugmansia genus are found on the streets of every neighborhood in San Francisco. These are represented by aromatic species like brugmansia arborea, brugmansia insignis, and brugmansia aurea — although the latter seems to be the most common.

All parts of these plants contain high levels of the tropane alkaloids hyoscyamine and scopolamine. The former is the toxin that gives Deadly Nightshade the title “deadly,” and the latter, scopolamine, is a powerful deliriant.

Deliriants are a subcategory of hallucinogens that induce a state of delirium in the user. Consuming as little as one leaf or flower can cause confusion, tremors, cycloplegia, and auditory and visual hallucinations. Users have reported seriously injuring themselves, attacking other people, and wandering around naked for hours — all without any awareness of their behavior.

An Erowid user reported that after consuming Angel’s Trumpets he “went to the bathroom to look at himself in the mirror… The reflection was normal, except for one thing: its eyes were closed! When I moved, the reflection moved. And when I touched my eyes, they were closed too.” …creepy…

Deliriant psychedelics are common both in nature and in your medicine cabinet. Plants like Jimson Weed (which I have come across frequently in San Jose, and is often considered the worst drug in the world), henbane, and mandrake are all deliriants, along with over-the-counter drugs like Benadryl and prescription pills like Ambien.

5. Castor Bean

Ricinus communis

400 Douglass St

The castor bean is the most sinister-looking of any plant on my list: it has large red palmate leaves with serrated edges and small clumps of seed pods covered in blood-red tentacles. It’s also the most poisonous: only a dozen of its small, grain-like seeds are enough to kill an adult.

Castor beans are deadly because they contain ricin. Ricin can be sprayed as a toxic dust and was weaponized by the US military during World War II (though it was never actually used). Ricin has been used in several murders and murder attempts. The Bulgarian dissident Georgi Markov was stabbed with an umbrella tipped with a ricin pellet, and President Bush was mailed letters containing ricin residue.

Despite its lethality, castor beans are common as ornamental plants and are grown to produce castor oil, which you can safely rub all over your body in the form of castor oil soap. Because of its usefulness and interesting appearance, castor beans can be found in parks and gardens throughout San Francisco.

6. Pokeweed

Phytolacca americana

4307 20th St

I discovered American Pokeweed growing in the shade of a small tree on 20th Street. Pokeweed fruits look like shiny, purple blueberries organized into grape-like clumps. Among all the plants on the list, it looks the most appealing and edible. However, it’s highly toxic to humans and other mammals.

All parts of the pokeweed plant are poisonous, containing phytolaccatoxin and phytolaccigenin, which are poisonous to mammals (but not birds). The juice of the berries can be absorbed through the skin. Some people have mistakenly thought that pokeweed berries are safe to eat after observing birds eating them, only to experience its powerful emetic and purgative effects. In high enough doses, pokeweed poisoning also causes convulsions and paralysis of the respiratory muscles, which can lead to death.

7. Field Bindweed

Convolvulus arvensis

599 McAllister St

The Convolvulaceae family (also called the Morning Glory family) contains over a thousand species of plants, including the sweet potato and hundreds of species of morning glory vines. Field Bindweed contains the alkaloid pseudotropine and can be dangerous for grazing animals, but human poisonings are not documented.

Morning glory species can be found on almost every block in San Francisco. An especially interesting species (which I was not able to identify) is the Mexican Morning Glory (Ipomoea tricolor). Ipomoea tricolor contains the alkaloid ergine (LSA) which has similar effects to the psychedelic LSD, although it has additional symptoms associated with alkaloid poisoning like nausea and vomiting.

Other Dangers

In seeking out the most poisonous plants in San Francisco, I also managed to identify many of the most poisonous plants in the world. Castor Bean, Poison Hemlock, and White Snakeroot belong on any list of poisonous plants. However, some especially deadly plants don’t seem to grow in San Francisco. These include Rosary Peas (Abrus precatorius), Deadly Nightshade (Atropa belladonna), and the Yew tree (Taxus baccata).

But the most deadly plant in the world is by far the most familiar: a genus of nightshades — called Nicotiana — are the source of tobacco, which kills almost half a million Americans each year.

Most plants growing in San Francisco are not toxic. And those that are are rarely deadly. Furthermore, the plants that are deadly do a good job of advertising their lethality: most people would never even approach a castor bean, much less put it in their mouth. During this journey I learned to stop worrying and love the poisonous plants that live among us.