Another option besides 'dressing' per se...

is that Arugula {Rocket} or Oxalis sp. have a strong acidity on their own and when minced fine in the salad, you won't need vinegar.

Magnolia or Daylilly or Nasturtium Blossoms or Watercress have a peppery flavour.

Pine needles chopped fine are also tangy and high in Vitamin C {though different species are decidedly better than others - all are edible}.

Beetroot blossoms/tops add a unique flavour.