Diversity of Rubiaceae in Ilocos Norte, Northwestern Luzon, Philippines: A Preliminary Checklist, Their Distribution, and Conservation Status

Abstract

The northern Cordillera Mountain Range of Ilocos Norte is an important site for floristic studies in the northwestern part of the Philippines. However, most of its forested areas remain understudied and limited data are available on the structure of its floristic communities. Here, a preliminary checklist of Rubiaceae species in Ilocos Norte is provided with notes on their distribution and conservation status. The field survey was conducted from April 2019 to March 2020 in Kalbario Patapat Natural Park (KPNP), Metropolitan Ilocos Norte Watershed Forest Reserve (MINWFR), and Mt. Lammin. A total of 57 species belonging to 28 genera and 15 tribes were recorded, which constitute 10.36% of the total number of Philippine Rubiaceae species. The genera with the highest number of recorded species are Psychotria, Ixora, and Ophiorrhiza with nine, six, and four species, respectively. Of these species, 27 are Philippine endemics that are widely distributed, and four species are endemic to the province. Among the sites surveyed, the tropical evergreen lowland rain forest of KPNP had the highest number of recorded species. With regard to their conservation status according to the IUCN (International Union for Conservation of Nature) red list category, one was assessed as Endangered. Moreover, based on the updated national list of threatened Philippine plants and their categories identified in the DENR (Department of Environment and Natural Resources) AO (Administrative Order) No. 2017-11, two are listed as Threatened species, one Critically Endangered, and one Vulnerable. According to the IUCN red list categories and criteria (2019), the four endemic species in the province recognized in the study are categorized as follows: one Critically Endangered (Antherostele callophylla), one Endangered (Psychotria tayabensis var. castanea), and two Vulnerable (Antirhea microphylla and Pyrostria triflora).