DENDROLOGY

Detailed explanation-1: -The keel is commonly formed in the flowers of beans, peas, grams, etc. of the family Papilionaceae. Hence, Beans are the correct answer.

Detailed explanation-2: -The keel is commonly found in the flowers of Papilionaceae plants such as beans, peas, and grains.

Detailed explanation-3: -Keel is the characteristic feature of the flower of plants belonging to the family Leguminosae/ Fabaceae. Indigofera belongs to Legumionosae.

Detailed explanation-4: -D) Calotropis. Hint:Keel is a characteristic feature of the flowers of family Papilionaceae. Keel is the innermost melded and fused petals, additionally called the carina. The keel is covered by the petals called wings which are themselves covered by a petal called standard or vexillum hunt.