The botanical name for this plant is written Vigna unguiculata (L.) Walp. The part that you are interested in, (L.) Walp., is called the author citation and indicates the first person (or people) who published the botanical name of the plant using the formally agreed upon International Code of Nomenclature.

In this case, the original scientific name designation is no longer considered correct so the original author is shown in parentheses and the new author appears after that. The names are abbreviated using standard abbreviations. L. refers to the famous botanist Carl Linnaeus and Walp. is Wilhelm Gerhard Walpers, a 19th c. German botanist.

You can read more about botanical nomenclature in our article "What is the Proper way to write a botanical name (Latin name)?"

Courtesy of NYBG Plant Information Service