I liked the podcast as well -- the first ATP podcast I've listened to... in fact, I think this might be the first podcast of any kind I've ever listened to. It's a brave new world! :)
I wanted to comment on sorrel and also list a couple of other perennial vegetables that I like. I've heard people use the term "sorrel" both for the Rumex species Dave and Trish mentioned on the show and for Oxalis species. They both share a lemony, tangy flavor, which I am guessing is why the share a common name.
The Rumex acetosa version(s) of sorrel come in a variety of species and cultivars, some with a history of cultivation (French sorrel, garden sorrel) and others more of an edible weed (sheep sorrel, R. acetosella). Usually they can be weedy, but there are non-flowering types available (e.g., 'Profusion' sorrel from Richter's Herbs) that, well, don't flower, and so don't make seeds and spread around. They can be multiplied through division. We have a bunch of these at our place and like them very much. Our little kids and all their friends absolutely ADORE it and go much on the leaves on a regular basis. We like to add it to salads--not as the main ingredient (too tangy for our tastes) but more than just as a complement. I'd say a ratio of 1/3 sorrel to 2/3 lettuces is about how we like it. We've also used it in place of spinach in spinach-feta pie, and it is fantastic.
One note of caution that I will reproduce here from the Plants for a Future website: "Plants can contain quite high levels of oxalic acid, which is what gives the leaves of many members of this genus an acid-lemon flavour. Perfectly alright in small quantities, the leaves should not be eaten in large amounts since the oxalic acid can lock-up other nutrients in the food, especially calcium, thus causing mineral deficiencies. The oxalic acid content will be reduced if the plant is cooked. People with a tendency to rheumatism, arthritis, gout, kidney stones or hyperacidity should take especial caution if including this plant in their diet since it can aggravate their condition." (
http://www.pfaf.org/user/Plant...)
Another perennial veggie I like is violets. Depending on the variety, their leaves can be perfect substitutes for lettuce in a salad. They will spread and make a nice ground cover if you let them--and why not?! The photo shows where I've let some violets form a ground cover under our plum tree, alongside some purslane--another item some people call a weed and that I call delicious.
Finally, a word in support of sea kale, Crambe maritima. This is in the cabbage family and can get pretty big, spreading some 3 feet across. It has gorgeous, large, wavy, blue-green leaves that are a decent substitute for kale or collards, especially raw. It also produces modest sized, broccoli-like florets that taste exactly like true broccoli when raw. It's the same size as the side shoots that some types of true broccoli form. To my taste, they develop a slightly bitter, off flavor when cooked, something that also happens to the leaves. I'd like to experiment with different recipes to see how to get them to come out right. I got to tell you, it is a real treat here in Vermont to have fresh "broccoli" from the garden in early May, same time as asparagus. Bonus 1: in my experience, they are totally immune to cabbage moth caterpillars, which I find on all my other (annual) brassicas. Bonus 2: if you let some of the florets go to flower, they fill the garden with a honey scent. Photos show a small harvest of sea kale leaves and "broccolis" and the plant in later-season glory.
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Did I mention it has never made an artichoke? Just like every year, I hope this is the year it does. 
I love how you have used violets and (delicious) purslane as a ground cover under your plum trees.
This is an awesome topic. I was so proud with my first pollination attempt!
