The crop that is dicotyledonous from the given options is Vigna unguiculata, also known as cowpea.
Dicotyledonous plants, also called dicots, are plants that have seeds with two cotyledons or embryonic leaves. These plants generally have broad leaves with veins that are arranged in a branched or net-like pattern.
On the other hand, monocotyledonous plants, or monocots, have seeds with a single cotyledon or embryonic leaf. These plants typically have long, narrow leaves with veins that are parallel to each other.
Among the given options, Zea mays (corn), Oryza sativa (rice), and Elaeis guineensis (oil palm) are monocotyledonous plants, while Vigna unguiculata (cowpea) is a dicotyledonous plant.
Cowpea is an important legume crop that is widely cultivated for its high protein content and ability to fix nitrogen in the soil. It is commonly grown in tropical and subtropical regions of the world and is used for food, feed, and forage purposes.