Kaiware Daikon (カイワレ大根) are sprouted daikon radish seeds. Frequently used in Japanese cuisine, such as in salads, sushi and as a garnish. These radish sprouts have a very powerful radish flavor with a real peppery finish. You can find them in Japanese and Asian grocery stores, usually in little clumps with roots attached shown in the image above (Source: GourmetSleuth.com).
Substitute: Alfalfa sprouts, radish sprouts