Nasturtium (Tropaeolum majus) grows everywhere - everywhere - in the Bay Area as well as many other parts of the country. It flourishes in parks, gardens, and along sidewalks pretty much year-round, except when it gets very cold or very dry. The plant is sprawling and iconic - even if you do not immediately know what I am talking about, you have probably seen nasturtium many times or perhaps tasted the flowers in a salad mix from the farmers' market or restaurant. The flowers are bright orange, yellow, or sometimes red with five petals on a single stem and leaves that look similar to lily pads, but thinner. The plant comes by way of South America and my guess is that it was transported here because it is so visually appealing, grows easily, and has a tasty, unique flavor.
What I love about the nasturtium plant is that with its mustard/radish/wasabi-like flavor and cheerfully spunky appearance, it is very approachable for even the biggest wild food skeptic (as long as said skeptic doesn't have an aversion to pungency). However, when you dig a little deeper, there are so many more possibilities than just using the fresh flower as a garnish or in salads. The leaves have a slightly thick, viscous quality to them, similar to okra, but I the sharp flavor cuts this a bit and the viscosity is helpful when you want to thicken a dish, such as a risotto or stew.
My first close and consistent experience with nasturtium was when I worked in a restaurant that used the flower to garnish mezza platters (hummus, tapenade, etc.). Being me, I would often grab a bunch of the leftover stems and take a big bite for a peppery "jolt" to keep me going throughout the night. On the other (more calculated) end of the spectrum, in the past few years I have been using the flowers in cocktails and experimenting with the leaves (either fresh in a salad or lightly cooked) and seed pods (pickling them is amazing - check out this recipe for California capers) Baby nasturtium flowers even made their way to the Noma menu when I had the opportunity to eat there and nasturtium pesto is a regular staple on the ForageSF Wild Kitchen dinners, or at least it was the few times I helped out.