Species richness and distribution of Hymenophyllaceae in  Mindanao Island, Philippines

Abstract

Hymenophyllaceae is the largest basal family of leptosporangiate ferns and is recognized as one of the major components of the epiphytic communities in tropical rainforests. Members of the family are distinguished morphologically from other ferns by their marginal involucre and lamina’s single-cell thickness. The specific environmental requirements of Hymenophyllaceae render them vulnerable to ecological and anthropogenic threats, as well as climate change. With the alarming rate of deforestation and the escalating climate crisis, this fern family faces extreme risk of population decline. Despite these challenges, Hymenophyllaceae remain understudied due to difficulties in identification; thus, data on their richness and distribution continue to be insufficient for conservation assessment. To address this, an extensive inventory of Hymenophyllaceae was conducted, supplemented by herbarium studies, to identify the species of Hymenophyllaceae and document their distribution in Mindanao, Philippines. Results revealed that 69% (42 taxa) of the total Hymenophyllaceae recorded in the Philippines were documented thriving in Mindanao including two endemic species Abrodictyum extravagans and Hymenophyllum edanoi. Elevational distribution of Hymenophyllaceae showed a hump-pattern, with increasing richness toward montane vegetation and gradually declining at higher mossy vegetation. Cephalomanes species has a restricted distribution, limited only to lower elevations (500–1000 m.) while the genera Abrodictyum, Crepidomanes, and Hymenophyllum were well-represented across varying elevations. The results of this study provide a comprehensive account of Hymenophyllaceae in Mindanao, highlighting the importance of conducting an extensive survey of this less-studied fern taxon.