wān is a bound form — it appears almost exclusively in
豌豆 (pea, Pisum sativum) and a small family of cooking compounds:
豌豆苗 (pea shoots / pea sprouts — a tender stir-fry green),
豌豆黄 (sweet pea paste, a Beijing palace snack),
青豌豆 (green peas, frozen-vegetable variety). On its own,
豌 is not used.