I'm a few weeks into my Ethnobotany class, working hard to learn all of the plants native to my area. At least some of these grow all over the place so this should be helpful to you even if you don't live in SoCal.
Someone on a listserv I'm on wrote that her yard was covered in stinging nettles and anyone who wanted some should come get them. So I did. I brought them home and put them in the bathtub to rinse them. I collected so many that they covered the entire tub.
Stinging nettles are edible and medicinal. After you dry them or cook them, they lose their sting. The trick is harvesting them and dealing with them until they are dried or cooked without getting stung too much. I've tried plenty of different methods, including oven mitts. Right now, my strategy involves tongs.
I tend to use them like spinach but I think their flavor is best in Italian tomato sauce dishes, like pizza or pasta. As a medicinal plant, they are diuretic and could lower blood pressure. They are also super nutritious. So toss some dried nettles into your favorite blend of herbal tea or into a soup!
Nettles develop a toxic compound when they grow large, so if you plan to eat them fresh, harvest them when they are 4"-8" tall. If you cut the plant off near the base instead of uprooting it, it will survive and you can get a few more harvests from it. Once the plant gets bigger, you need to dry it in order to use it, because that gets rid of the toxins in it.
After rinsing off my big haul of nettles, I lifted them out of the tub one by one with tongs and sorted them into piles by size. I hung the big ones upside down to dry, and set the little ones aside to eat later.
Just a note if you're eating nettles - cut the leaves and tops off the stems and eat those. The stems will be fantastic for your compost pile. Nettles have historically been used as a source of fiber to make clothes. If you've ever tried to cook and eat a large thick nettle stem, you'll understand why!
Some of my nettles, hung in upside down bundles to dry on either side of my window. I've got more hanging outside, and I got about 3 or 4 meals out of the ones I ate fresh.
California Black Walnut
The California black walnut's flowers, shown in the top photo, are catkins. Another plant with catkins that you are no doubt familiar with is the willow. Those things you called "pussywillows" when you were a kid? Those are catkins.
Historically, California Indians near LA made extensive use of the black walnut, but they used the shells more than they used the nuts. (And no, they didn't eat the shells - they put them to other uses.)
Mature leaf with flower in the center
Miner's lettuce is edible. Eat it before it flowers. After that it gets bitter.
The species shown here is Claytonia perforliata, and it was brought from near Malibu. In San Diego county, you can find C. parviflora, which has a slightly different shaped leaf.
Top side of leaf
Underside of leaf
If you go to the store and buy mugwort, you'll get Artemisia vulgaris. The local species, shown here, is A. douglasiana. It's about five times as strong as what you get in the store. You can find it growing in riparian areas near water, often in thick stands that grow several feet tall. The top of the leaves are green, the undersides are silver.
Often, mugwort grows near poison oak. If you touch poison oak, then wipe your body with mugwort to get the poison oak off. But I would still go straight home and scrub your entire body with soap and put your clothes in a plastic bag and not touch them til they've been washed several times just in case
Indians also used this as a bronchial and sinus decongestant, and an eyewash. They used it to get rid of intestinal parasites, used it during sweats, and used it ceremonially. I don't have details on those latter uses BUT I do know that it's popularly used now to stimulate vivid dreams. You can eat it, drink it (as a tea), smell it, or smoke it, and you'll have extremely vivid dreams. However, I've read some stuff that made me feel cautious about eating it or drinking it, and I doubt smoking it is healthy either. So I'd go the aromatherapy route. I gave this stuff a good sniff as we passed it around for class. I don't know if the mugwort's to blame, but I've had the most incredibly vivid dreams all week ever since then.
Fuschia Flowered Gooseberry
These aren't the best pictures. My hunch is that this one's edible, although I don't know how good it would taste. I've been doing a no-no when it comes to currants and gooseberries. I've been recognizing them by their leaf-shape. The most accurate way to recognize an unfamiliar plant is by the flower. Unrelated plants can have similar looking leaves because they live in the same environment and they are adapted to the same conditions - but the reproductive structures of a flower are what truly give a plant's identity away. And I've been a bad girl because I took one look at the shape of these leaves and said "Currant?" Gooseberries are related, so it was a really good guess.
I'll leave you with these for now. I'll have more for you soon. And I'm now planning a camping trip to Joshua Tree this spring, which means I'll be able to see plants from other nearby ecosystems - Juniper-Pinyon Pine woodland, black oaks, Mojave desert plants, creosote bush, and more!!!!