1. A plant species identification apparatus for identifying plant species, the apparatus comprising a processor configured to perform a process including: storing reference spectral data which indicate a reflectance spectral feature classified by area segments including a sunlit portion and a shaded portion in addition to the plant species, to a reference data storage part; predicting, from the reference data storage part, a reflectance spectrum of an area where the sunlit portion and the shaded portion are mixed at a predetermined ratio based on the reference spectral data that are for a same plant species and that are classified into the area segments including the sunlit portion and the shaded portion, classifying a set of the reference spectral data indicating a predicted reflectance spectral feature into the same plant species and a mixed portion of the area segment, and adding the set of the reference spectral data to the reference data storage part; acquiring hyperspectral data to be a target; specifying most similar reference spectral data to a feature of reflectance spectrum of a pixel for each of pixels of the hyperspectral data from the reference data storage part; and determining the plant species of the pixels based on a classification of the reference spectral data.