Prickly pear species. Their taste probably wouldn't appeal to the average American's palate,

San Diegans who refer panhandlers to St. Vincent de Paul Village or the Rescue Mission may not know about San Diego's third option for free food: the local canyons.

Jon Rebman, Ph.D., the curator of botany at San Diego's Natural History Museum, says that much of the plant life that grows in San Diego's canyons and back yards is perfectly edible. "I'm not saying it would be easy to live off the plant life here. It's not just the public areas but private too. Think of all the different things that are planted, the different types of trees. You can grow just about anything here. All the citrus...then you've got things like loquats and all sorts of edible fruits that produce throughout the year."

Rebman, 37, works in the taxonomy of plant species and specializes in the deserts of Baja California, where he leads research expeditions every two years. When discussing edible plants, his fascination with cacti is apparent. "Most of them have edible fruits. The pads are edible. In Mexico, they call that the nopalitos. And the fruits, or tunas, are extremely edible. Nopalitos are the pads on a couple of species of prickly pears, and they are a major food in Mexico. You can boil them, dice them up and use them with eggs, or eat them alone as a side dish. They're supposed to be good for diabetics."

Cactus pads may be mainstream food for Mexico, but Rebman admits that their taste probably wouldn't appeal to the average American's palate, although the fruits would. "They are really important. I always go back to Illinois and tell them, 'I just had tuna ice cream and it's fantastic!' And they just cringe, thinking I mean the fish!" he laughs. "But you can make juices out of it, or you can eat it straight. It's a big, large fruit, and it tastes kind of like a watermelon. It's very sweet and tasty, and they're producing a lot. It's a major industry for Mexico."

Another cactus species Rebman recommends as edible is the agave. "There's a lot of them in Balboa Park, on the desert side. There used to be agave-roasting pits, where the indigenous people used them extensively. That's where tequila, mescal, miel, pulque, and all those other beverages come from. It's an edible stem portion. You take off all the leaves and roast this rounded stem-like thing. It looks like a pineapple without the leaves, so they call it a piña in Mexico. That starch then becomes available after it's roasted, kind of like a potato."

There's a lot more to eat growing around San Diego than just cacti. Native elderberries are found in most of the urban canyons. Live oak acorns are edible but require more effort than most people would be willing to exert. "You have to keep them in bags of water for a long period of time. You have to leach them like olives, to get the tannins out, a type of chemical that is real tart and nasty."

There is a native buckwheat, but it has little in common with the grain used for buckwheat flour. "You always hear about buckwheat in the health-food stores, but that's not the native kind from around here. That's an old-world species."

Other edible species include yucca flowers and amaranth seed. "The local indigenous people used to harvest the seeds and crush it into a meal. It's still used as a grain source, and you can find it in some health-food stores. I believe it's still popular in Mexico."

Part of Rebman's work with the museum includes leading nature walks, a place where he makes it a point not to mention the edible plant life, as some different plant species look quite similar, and a mistake can be lethal. "We have so much diversity here in San Diego County that it's easy to get confused. Things can look very much alike. One of the common things we have in our area are these white, umbelliferous plants that have these white flowers. The wild carrot looks like that, but once every few years, you'll see an article where somebody confused hemlock for the carrot and dies. It's that toxic. Think about Socrates!"

Milkweed is another local poisonous plant, but no one has ever been known to eat it. Castor beans are extremely lethal. "That's a common weed species that we have in most urban canyons. In fact, a chemical came in vogue that is derived from the seed called ricin, and it's one of these powders that is tasteless and has no smell. About ten years ago, there was a story about somebody putting it on the end of an umbrella and jabbing someone. Once it gets into the bloodstream and breaks down, you can't even tell what killed the person."

Offroaders in San Diego's backcountry often find leafy vines with a green hanging fruit covered with long, soft needles. "That's wild cucumber. I don't think the fruits are edible, but underneath the ground is a huge tuber, or stem body. It's basically one of these things where you'll see the vines coming up after a fire. They come from this huge underground starchy reserve, and it is edible. It's kind of like a potato. You'd have to roast it."

While aware of the many books used as guides to eating native plants, Rebman is reluctant to recommend any because of the danger of misidentifying plants. "There's a lot of them like Eat the Weeds [by Charles Harris], for example. We're in an age where people want to get back to nature. Some books are all right, but a lot of them... I'll give you a warning: I don't suggest them because of the diversity of our region and the confusion you can have with things that are edible and things that are not. A lot of these books are done by amateurs, and they use common names, which are misleading. Sometimes they're for regions other than Southern California -- maybe something from back East that doesn't occur in our area, and you'll find something that looks similar and think it's edible. And common names are very misleading. One species can have many different common names, or you can be using the common name for many different species that are not related at all. Those books can be real dangerous.

"A lot of the edible stuff is derived from indigenous cultures, but most of ours are gone. And most of the information on what was used has been lost. So that knowledge is not readily available. The kinds of places where you would find that information would be in scientific texts."

Poison oak is an example of a nonedible plant that Rebman uses to show how easily one can be confused by the similar-looking plants. "There's a lot of other things like it that are not poisonous but are native and have the three leaflets. We might think they're poisonous because of how they look, but they're not."

Just how diverse is San Diego's plant life? Besides having the most diverse terrain of any county in the United States, San Diego is the most diverse county in native plants as well. "Because of this mild climate, we can grow a lot of tropical things like fruits. Guavas and papayas can actually grow in our yards because we don't get the freezes. We have to be at the top in our ability to grow things that are edible, as far as horticulture is concerned. I'm not a horticulturist; I'm more interested in plant taxonomy. But the percentage of plants that are edible is going to be a lot higher here than in most other places. But that cuts both ways -- we might also have the highest percentage of poisonous plants! I can't say that for sure, but it's a possibility."

Next to Rebman's office on the top floor of the old section of the museum is the San Diego botanist's holy of holies: The Synoptic Collection, a vast room filled with sample specimens of virtually every native plant in San Diego County. Some of the specimens date back to the 1920s. As he opens one of the lockers, Rebman finds a file with samples of wild carrot from 1938. He opens another file with a sample of hemlock. To the untrained eye, they look identical. "These are both white and have a flower. When dissected, they look a lot alike. You can see the similarity in the leaves. The wild carrot is not always big like this." He pulls out a sample with smaller flowers.

Pulling some more files, Rebman proffers a flattened-looking cactus with its fruit looking like an exploded prune. The sample is dated from 1939, labeled "Mission Prickly Pear." "This is edible as well. You'll see them getting those bright red flowers on them. The fruit has been cut and splayed. A lot of people refer to them as 'Indian figs.' This comes from a higher elevation, but you can see some of the red is still in there. It is very pulpy when fresh." He opens another file with a similar, thinner-looking sample. "Here's another prickly pear species, and it's edible as well. It's not a native plant, but it ended up in a lot of our canyons. People just kind of threw a pad over the fence, and it soon became a forest."

Probably no park in San Diego offers as much horticultural diversity as Balboa Park, but using the park as a source for food would not only taste bad, it would also be illegal. Michael Ruiz, the senior park ranger at Balboa Park, says that plant- and seed-gathering permits are issued rarely. "We do have them, but it's very strict. It would be primarily for entities like the Natural History Museum, who would use it for educational or research purposes. We just don't want anyone coming in here and gathering plants. What happens is that they gather them for their own profit or to save a trip to the nursery to buy cactus. We don't set the fines for that, and they change quite often. That's established by the courts. If a citation is issued, then the fine is established by the judge."

Plant life is not the only wild urban food source. Most of the local species of rabbits, gophers, rats, and pigeons are edible, but Rebman does not suggest anyone satiate their appetite by hunting in the city. "Don't ever think I suggested any of that! You could eat them if you were really desperate, but I don't recommend it."