While reliance on morphology has been at the expense of clearly distinguishing gracilarioid species, molecular data have proven to be more reliable in discriminating between taxa. Gracilaria phuquocensis was originally described, based on materials collected from Vietnam. Since it was described in 2020, there have been no further reports of this species. Meanwhile, a question has been raised as to whether the identity of a rhodophyte gracilarioid alga collected from the Philippines that has been referred to as an unidentified species of Gracilaria, could be G. phuquocensis. Based on comparative morpho-anatomical features and a molecular phylogeny based on rbcL gene sequences, establishing the identity of the Philippine material has led to the finding of the new record of G. phuquocensis outside its type locality. In addition to the discovery of G. phuquocensis in the Philippines, the species here is also identified as a newly-reported host for the adelphoparasite resembling Gracilaria babae.

Agarophyte, distributional records, Gracilaria babae, rbcL, taxonomy

Members of Gracilaria Greville are a major source of agar, a valuable substance widely used in various industries (Torres et al. 2019; Mantri et al. 2023). The genus has over 270 currently-recognised species worldwide (Guiry and Guiry 2023), a number that continues to increase with new taxonomic work (Freshwater et al. 2022; Saengkaew et al. 2022; Wang et al. 2023). As gracilarioids have relatively low morphological diversity and are speciose, discrimination between taxa is better achieved using combined morphological and genetic data (Lyra et al. 2015; Gurgel et al. 2018; Lyra et al. 2021).

Gracilaria phuquocensis N.H. Le, N. Muangmai, G.C. Zuccarello was established based on a specimen collected from Phu Quoc Island in Vietnam (Le et al. 2020). The application of the name became important for the taxonomic clarification of some flattened gracilarioids, which vary in blade dimensions, number of medullary cell layers and tetraporangial features. The use of morphology in combination with molecular data indicates that G. phuquocensis is a separate species. However, a question remained regarding the distribution of G. phuquocensis beyond its type locality. Using a molecular-assisted alpha taxonomic approach, here, we confirm the presence of G. phuquocensis in the Philippines.

Gracilaria phuquocensis from Vietnam had been previously identified as Gracilaria mammillaris (Montagne) M. Howe. However, G. mammillaris is considered to have a wide distribution in the western Atlantic (Gurgel et al. 2004), extending to occurrences in Venezuela and Brazil (Hardesty and Freshwater 2018), and a previous study by Le et al. (2020) as well as our recent research (Fig. 2) indeed confirmed that the Vietnamese material was phylogenetically distinct from G. mammillaris. The recognition of G. phuquocensis as a distinct taxon helps to provide a better base line for comparing Vietnamese specimens of Gracilaria cuneifolia (Okamura) I.K. Lee & Kurogi, Gracilaria yamamotoi Zhang & B.M. Xia and Gracilaria rhodymenioides A.J.K. Millar, as these Gracilaria species are representative of taxonomically challenging complexes. While the current Philippine records only confirm the presence of G. phuquocensis amongst these flattened gracilarioids, some or all of the other species may be present in the area, but not recognised on morphological characters alone, especially since the macroalgal flora in the Philippines and Vietnam has high similarities in terms of species composition (Nguyen et al. 2013).

The presence of an adelphoparasite resembling Gracilaria babae observed for the first time in G. phuquocensis, increases the number of gracilarioid species from which such neoplastic parasites (sensu Salomaki and Lane 2019) have been reported. Gracilaria babae is only known to be associated with Gracilaria salicornia (C.Agardh) E.Y. Dawson (Yamamoto 1986) and an unidentified species of Gracilaria reported as Hydropuntia sp. (Ng et al. 2014). However, until molecular studies are undertaken, the identity of the species on G. phuquocensis remains unconfirmed.

Our study suggests that the Philippines seems to present hidden diversity of gracilarioid species, at least in the southeast Asia (Phang et al. 2021; Saengkaew et al. 2022; Nguyen et al. 2023). The latest reports for gracilarioid species in the Philippines prior to this study had six new records (Lastimoso and Santiañez 2021). Adding G. phuquocensis, this study brings the number of recorded Philippine gracilarioids to 46 taxa.

Yet another concerning issue is that the taxonomic accuracy underpinning gracilarioid names need updating (see Lyra et al. 2021). More attention must also be given to species that remain to be described or are overlooked. The number of gracilarioid species thus far reported from the Philippines (see Lastimoso and Santiañez 2021) appears to be inflated. Over the years, several workers, many of whom were working at a time when taxonomic concepts were based on doubtful morphological characters, have added records to the local flora, often using names for species found outside the Indo-Pacific Region. For example, Gracilaria venezuelensis W.R.Taylor was reported from the Philippine (Westernhagen 1973) and subsequently included in a number of Philippine catalogues and checklists without being verified. However, it was considered to be restricted to the Caribbean Basin (Gurgel et al. 2004), although there is always the possibility of the presence of non-indigenous species in the Philippine flora. This underscores the need to check available vouchers and to add records in the future that are backed by morphological and/or molecular data.

We are grateful to Jomari D. Dig for his assistance during field collections. We are also deeply grateful to Suttikarn Sutti for helping with the deposition of voucher specimens at the National Science Museum in Thailand.