Garden nasturtium (Tropaeolum majus) is a sprawling South American annual grown both as an ornamental and as a wholly edible plant: its vivid orange, yellow and red spurred flowers, round shield-shaped leaves and green seed pods all carry a bright, peppery, watercress-like bite. The flowers brighten salads and plates, the leaves add a mustardy snap, and the unripe seed pods are pickled as a caper substitute.