Inventory of Vascular Lithophytes in an Inner Wall Section of Intramuros, Manila, and a New Distribution Record for Pteris ryukyuensis

Intramuros is one of the heritage areas in the Philippines that could host a diverse range of plant species such as vascular lithophytes due to its old, mossy, rocky walls that were once used to protect the city from invasions and attacks. However, the lack of studies concerning the presence of vascular lithophytes raises questions about their adaptations, diversity, and environmental significance in urban ecosystems. This study aimed to identify vascular lithophytes on Intramuros's inner wall and assess their abundance, diversity, endemicity, and conservation status. By examining plants adapted to this unique urban habitat, the study offers insights into their ecological roles and significance, contributing to a deeper understanding of urban biodiversity and the conservation potential of heritage sites. This survey, conducted from April–May 2024, identified 25 species exhibiting varied lithophytic habits, with Pilea microphylla and Lindenbergia philippinensis emerging as the most abundant epilithic species. Twelve (12) out of 25 recorded species are native, whereas the rest are exotic (naturalized or cultivated). Except for the strict lithophyte Pteris ryukyuensis, all species exhibited lithophytic tendencies. In contrast, the abundance of Ficus, represented by four species, suggests adaptation and ecological role within the wall ecosystem of Intramuros. Populations of previously considered vulnerable species such as the endemic Ficus ulmifolia were found at different wall portions. Importantly, this study reveals an extended range of P. ryukyuensis in the Philippines, marking its first recorded presence outside the Batanes Islands in over 60 years.