46 Philippine Journal of Systematic Biology Vol. VIII (June 2014) 1 School of Natural Sciences, Saint Louis University, 2600 Baguio City, Philippines; 2 Pangasinan State University, Lingayen, Pangasinan; 3 Korean Lichen Research Institute, Sunchon National University, Suncheon, Jeollanam’do, South Korea *Corresponding author: paulinabawingan@ymail.com This study is a survey of corticolous lichens in the Hundred Islands, Philippines noting their diversity and morpho’anatomical adaptive features. There were only six islands visited due to accessibility and safety reasons. There are at least thirty’two identified species of lichens; majority is crustose dominated by Graphidaceae lichens followed by pyrenolichens in terms of diversity. Morpho’anatomical features considered to be adaptive include crustose and narrow’lobed foliose growth forms, homiomerous thallus organization, thick upper cortex, and presence of pruina in the cortical or medullary layers. KEYWORDS: Hundred islands, epiphytic lichens, adaptive features Lichens are symbioses of heterotrophic fungi (mycobiont) and photosynthetic algae and/or cyanobacteria (photobiont) that must be beneficial to and adaptive for the organisms involved considering that 85% of fungi have resorted to this type of existence (Honegger, 1996). It is known that lichenized fungi have developed complex vegetative structures that enable them to withstand harsh conditions of the environment (Kappen, 1973, 1988). The appearance of lichens is primarily determined by the mycobiont. Lichens generally exhibit three main growth forms: the leafy foliose, the shrubby or hairy fruticose, or the crust’like crustose type. Believed to have been formed two hundred million years ago, the Hundred Islands is a cluster of islands located in the Lingayen Gulf (16 o 12 ’ N, 120 o 2 ’ E) in the province of Pangasinan, northern Philippines (Fig. 1). It is