Arriola, Axel H., and Grecebio Jonathan D. Alejandro. 2013. “A New Species of Villaria (Octotropideae, Rubiaceae) from Luzon, Philippines Including Its Conservation Status”. Phytotaxa 111 (1). Auckland, New Zealand:57–60. https://doi.org/10.11646/phytotaxa.111.1.5.