The M. truncatula apetalla, or tap, mutation results in male sterility, due to homeotic conversion of floral organs. Here, a tap flower (a) is compared to a wild type (A17) flower (b). The floral whorls are indicated by numbers, where in wildtype, 1 = sepal, 2 = petal, 3 = anther, and 4 = carpel. In tap, whorl 3 is composed of petaloid, sterile anthers.
Figures courtesy of Varma Penmetsa and Doug Cook.