(Photo courtesy of Rene Alfred Anton Bustamante)

A new Philippine species of Ridsdalea (Rubiaceae, Ixoroideae) has been discovered in karst vegetation in El Nido, Palawan.

The species was described by Rene Alfred Anton Bustamante and Dr. Pieter Pelser in the scientific journal Blumea, an international journal on the biodiversity, evolution, and biogeography of plants, published on January 17.

Bustamante, who started to explore and document the flora of El Nido in 2017, told Palawan News on Wednesday that it is “unique” among Malesian Ridsdalea species in possessing a corolla tube that is noticeably inflated at the apex, a feature also shared by R. sootepensis and R. thailandica from Laos and Thailand. He noted that its flowers are smaller, and the anthers do not emerge from the corolla tube, as opposed to both of these species.

(Photos courtesy of W. Cabanillas & L.M. Camangeg; P.B Pelser & J.F Barcelona.)

“It is unique among Malesian Ridsdalea species in having a corolla tube that is distinctly inflated at the apex, a character state also displayed by R. sootepensis and R. thailandica from Laos and Thailand. Amongst others, R. philippinensis, however, differs from both of these species in having smaller flowers and anthers that do not emerge from the corolla tube,” he said.

Researchers describe the new Ridsdalea species from Palawan as Ridsdalea Philippinensis. It is the Philippines’ seventh Ridsdalea species and the third to be found on the island of Palawan.

The Philippine Taxonomic Initiative (PTI) Inc., a non-government organization (NGO) based in Barangay Maligaya, El Nido, Palawan, had organized several other scientific excursions around Palawan with support from an increasing number of Filipinos.

“PTI relies heavily on local funding from individuals, organizations, and collaborations with local artists. The organization is proudly supported by a growing number of Filipinos with a passion for conservation and exploration. However, we also apply for funding from international grant-giving bodies. Recently, we were awarded a grant from the American Begonia Society that will fund a series of expeditions into Nueva Viscaya,” Bustamante said.

The discoveries were made in the karst forest in El Nido by Rene Alfred Anton Bustamante and Pieter Pelser, whose study was published on January 17, 2022.

Karst is a landscape formed by the weathering of calcium-rich rocks such as limestone, dolomite, and gypsum. Karst formations account for 12% of the total land area in the Philippines and contain a high level of plant endemism.

According to the study, the inaccessibility of karst topography makes field study difficult, so species diversity in karst locations is likely to be underestimated. The Caramoan Natural Park Protected Area (CNPPA) in Camarines Sur Province, the Puerto Princesa Subterranean River National Park (PPSRNP), and Saint Paul Mountain Range, both in Palawan, and the Chocolate Hills Natural Monument in Bohol are all notable forests over limestone places in the Philippines. The karst terrain at El Nido, Palawan, is mostly made up of exposed, vertical limestone cliffs.

“The discovery of this new species shows how special, but poorly known the karst ecosystems of the Philippines are and, therefore, how important it is to protect them,” Dr. Pieter Pelser, botanist and co-author of the paper.