This potato salad calls for just a small amount of mayonnaise, letting the unconventional ingredients -- horseradish-like sea rocket and tart sour grass -- shine through.
Place potatoes in a large pot, and cover with water by 2 inches. Add 1 tablespoon salt. Bring to a boil. Reduce heat, and simmer until potatoes are tender when pierced with the tip of a paring knife, 10 to 12 minutes. Drain, and transfer to a large bowl. Let cool for 15 minutes.
Toss potatoes with oil, mayonnaise, and vinegar. Season with salt and pepper. Sprinkle with sea rocket and sour grass; toss to coat. Serve immediately.