How many plants among Indigofera, Sesbania, Salvia, Allium, Aloe, mustard, groundnut, radish, gram and turnip have stamens with different lengths in their flowers?

Among the given options, turnip and Salvia have didynamous and radish and mustard have tetradynamous stamens. Didynamous stamens refers to presence of four stamens (two longer and two shorter). Tetradynamous stamens are stamens of different length present in two whorls. Therefore, the correct answer is option D.