Peel artichoke stems. Cut off top  1/2 inch of 1 artichoke with a serrated knife. Bend outer leaves backward until they snap off close to base, then discard several more layers of leaves in same manner until you reach pale yellow leaves with pale green tips. Cut off green tips. Trim dark green fibrous parts from base and sides of artichoke with a small sharp knife, then cut in half lengthwise and thinly slice; drop slices into acidulated water. Repeat with remaining artichokes.

From orange, zest enough peel to make 1/2 teaspoon; place in a large bowl. Using a sharp paring knife, cut peel and white pith from oranges, then cut each section of fruit away from membrane, cutting as close to membrane as you can. Cut sections in half crosswise and set aside. Squeeze enough juice from membrane to make 1/4 cup; add to bowl with zest. To orange juice mixture, add oil, 1/4 teaspoon salt and pinch pepper; whisk together dressing.

Drain and pat dry artichokes; add to bowl with dressing, toss to combine and let stand 10 minutes. Add orange sections, endives and walnuts; gently toss to combine.