Guide to Philippine Flora and Fauna
Natural Resources Management Center, Ministry of Natural Resources and University of the Philippines; Distributed by Goodwill Bookstore

The Green Guide : A Sourcebook on the Philippine Environment
This is the best guide to the state, issues and vision of the environment.

The Complete Writings of Dr. Eduardo A. Quisumbing on Philippine Orchids
Eduardo A. Quisumbing / Hardcover/ Published 1981 / American Orchid Society. Two-volume set. Quisumbing is the foremost authority on Philippine Orchids. For stamp vignettes, see A1962C09, A1993H14 and souvenir sheets: A1993H14S1, A1993H14S2, A1993H14S3, and A1993H14S4.

A Pictorial Cyclopedia of Philippine Ornamental Plants
Domingo A. Madulid
A very good resource for ornamental plants in the Philippines. Colored and black-and-white pictures are also included.

Plants That You Know But Really Don't : Home Remedies from 110 Philippine Medicinal Plants
Some of these plants have been featured as stamp vignettes, see A1992B04