Gladiolus and dahlias are spring-planted and summer-flowering bulbs, but they are entirely different plants. The first difference is in their taxonomy. Glads belong to the Iridaceae family, whereas dahlias come from the Asteraceae family. Dahlias are native to North and Central America, and gladioli originally grew in South Africa and Europe. Dahlia flowers resemble daisies and have one row of petals. Dahlias have peony-like flowers and contain two or more rows of petals surrounding the center. On the other hand, gladioli produce flowers that resemble trumpets on the flower stems.