An integrative taxonomic approach deciphers a cryptic species of marine alga from Indonesia, Ptilophora legalliae sp. nov. (Gelidiales, Rhodophyta)

ABSTRACT Diversity of tropical gelidioid algae is often overlooked due to the superficial similarity even between species of different genera. Specimens of Indonesian Ptilophora previously identified as P. scalaramosa were collected on three islands in the Indonesian archipelago and compared to P. scalaramosa specimens collected from the species type locality in Bulusan, the Philippines. An integrative approach utilizing morphological and genetic data demonstrated that the Indonesian specimens represent two species, one herein described as P. legalliae sp. nov. Ptilophora legalliae can be distinguished from P. scalaramosa and other Ptilophora species by this combination of traits: plants fasciculate from rhizomatous holdfast, short alae on the middle part of erect axes, short pinnules, with 2–3 layers of outer cortical cells. Ptilophora legalliae inhabits intertidal to subtidal rocky substrates in Indonesia, while P. scalaramosa occurs consistently on subtidal substrata in the Philippines. Phylogenetic analyses of rbcL places P. legalliae with high support as sister to the subclade of Ptilophora sp. from Indonesia and P. scalaramosa from the Philippines, suggesting that these species likely diverged from a common ancestor in Southeast Asia. This study emphasizes the necessity for molecular approach to decipher the hidden diversity of red algae in Indonesia and adjacent regions.