"Stewartia pseudocamellia... is recorded as a host plant for [the sawfly species] E. nigromaculata and E. vernalis." 
"Stewartia pseudocamellia (Japanese Stewartia)... is an excellent garden plant with ornamental features for all four seasons. Reproduction difficulty, however, limits its popularity." 
"Several parts, such as the bark, stem, and fruit have been used as folk medicines to treat circulatory disorders, hepatitis, hepatocirrhosis, and paralysis of the limbs and pain related problems." 
A range of compounds isolated from this plant may prove useful in developing an anti-melanogenic drug. 
 Nair, A., Zhang, D., Smagula, J., & Hu, D. (2008). Rooting and overwintering stem cuttings of Stewartia pseudocamellia Maxim. relevant to hormone, media, and temperature. HortScience, 43(7), 2124-2128.
 Seong, Z. K., Kim, H. S., Won, Y. M., Kim, J. L., Song, H. H., Kim, D. Y., ... & Lee, H. K. (2016). Phenylacylphenol derivatives with anti-melanogenic activity from Stewartia pseudocamellia. Archives of pharmacal research, 39(5), 636-645.