Keel is characteristic of the flowers of

Explanation

(d): The flowers of Family Papilionaceae have butterfly-shaped corolla (papilionaceous corolla). The posterior or outermost petal is the largest and is called standard or vexillum, two lateral petals are similar and generally clawed, are called wings or alae and the two anterior petals called keel are fused enclosing stamens and carpels. This type of petal arrangement is found in beans, grams, peas, Indigofera, etc