Hedyotis hamiguitanensis (Rubiaceae: Spermacoceae), a new species from Mt. Hamiguitan, Davao Oriental, Philippines and its systematic position in Hedyotis

Hedyotis hamiguitanensis, from Mt. Hamiguitan, Davao Oriental, Philippines, is described, illustrated, and compared with two similar species, H. whiteheadii and H. schlechteri. This species is distinguished from congeneric Philippine species by its 5–12 cm long, compound, umbellate inflorescences, pendulous flowers, lanceolate to oblanceolate, thick, scabrid leaf blades with revolute margins. Its phylogenetic systematic position within the tribe Spermococeae is determined with a phylogenetic analysis using chloroplast (rps16, petD) and nuclear ribosomal (ITS, ETS) nucleotide sequence data.


INTRODUCTION
Hedyotis Linnaeus (1753: 101) is part of the Hedyotis-Oldenlandia complex, a taxonomically confusing group that was formerly placed in the tribe Hedyotideae, which is now part of tribe Spermacoceae (Bremer 1996;Andersson and Rova 1999;Bremer and Manen 2000). The genus has long been controversial because of the lack of taxonomic delimitation and molecular data (Terrell and Robinson 2003). Recent phylogenetic analyses based on nuclear and plastid sequences of Asian-Pacific taxa from this group have identified 13 well-supported monophyletic genera (Neupane et al., 2015). Diagnostic characters such as habit, fruit type, seed form, and pollen type were compared to the phylogeny for characterizing the clades (Kårehed et al 2008;Groeninckx et al. 2009;Guo et al. B 2013;Wikström et al. 2013;Neupane et al. 2015). In the latest revision (Neupane et al. 2015), members of Hedyotis s.str. included species from Sri Lanka, India, SE China, Indo-Chi-na, Malesia, Papuasia, Northwest Pacific, and Australia. The recent studies lack Hedyotis species occurring in the Philippines . Hedyotis is characterized by its habit -suffrutescent herbs, shrubs, or small trees -, its capsules with apex not protruding beyond the calyx lobes, the septicidal dehiscence usually followed by a partial apical loculicidal dehiscence that sometimes results in two semi-split valves and, the dorsiventrally compressed seeds (Wikström et al. 2013). The flowers have a pubescent corolla tube and pollen with 3 -4 ecto-apertures, endoapertures shaped as an endocingulum and a tectum with a double reticulum pattern (Neupane et al. 2015).
During fieldwork of the Thomasian Angiosperm Phylogeny and Barcoding Group (TAPBG) on Mt. Hamiguitan, Davao Oriental, Philippines, an interesting taxon was discovered. Two populations were observed, one in mossy forests and the other in pygmy forests on the same mountain. The collected material is morphologically similar to Hedyotis whiteheadii Merrill (1907: 303) and H. schlechteri Merrill & Perry (1945: 1), but detailed comparison showed that these two species differ from the newly collected material by their vegetative and inflorescence morphology. Therefore, a new Hedyotis species is here described and illustrated. We also included the new species in a maximum likelihood and Bayesian phylogenetic analysis of Hedyotis s.str. (sensu Neupane et al. 2015) based on chloroplast (rps16, petD) and nuclear ribosomal (ITS, ETS) nucleotide sequence data to elucidate its position within the genus.

MATERIAL AND METHODS
Hedyotis specimens were collected in the forests of Mt. Hamiguitan, Davao Oriental, Philippines, on 15 April 2017. Measurements, colors and other details given in the descriptions are based on field observations, herbarium specimens and reproductive parts preserved in 70% ethanol. Microscopic features were analyzed using a dissecting microscope (Olympus SZ2-ILST). Measurements were obtained using a metric vernier caliper. Character state terminology is based on Beentje (2010). Hedyotis specimens from different herbaria (A, CAHUP, K, PNH, PUH US, and USTH) were compared to our specimens. Additional specimens were examined on JSTOR Global Plants (https://plants.jstor. org/, accessed 18 May 2021). Herbarium specimens were deposited in USTH.
For the molecular data, DNA was extracted from silica gel-dried leaves using the DNeasy Plant Mini Kit (Qiagen, Germany) following the manufacturer's protocol. The amplification protocol for nuclear and chloroplast regions follows Kårehed et al. (2008: 845) and Groeninckx et al. (2009: 111), respectively. The alignment file was downloaded from the supplementary data provided by Neupane et al. (2015). A total of 293 accessions were analyzed with the addition of 2 samples from this study, H. hamiguitanensis CB177051 and CB17036. The new sequences from plastid (rps16, petD) and nuclear (ITS) regions of H. hamiguitanensis produced during our investigation were deposited in Genbank (Genbank accession numbers MZ407950, MZ435801, MZ435799 for USTH016306 MZ407951, MZ435802, MZ435800 for USTH016305 respectively) Sequences were edited and pre-aligned using CodonCode Aligner v.4.0.4 (Codon-Code Corporation, Dedham, MA) and subsequently aligned using MAFFT v.7 (Katoh and Standley, 2013). The alignment was manually adjusted using SeaView Sequence Aligner V.4 (Guoy et al., 2010

Diagnosis
Hedyotis hamiguitanensis is similar to H. whiteheadii and H. schlechteri because of general leaf size ranging from 1.5-4 cm with 3-4 lateral nerves, densely hirsute petioles, and compound peduncled inflorescence, from which it can be distinguished by its lanceolate to oblanceolate, relatively thick leaves, scabrid surface, margins that are entire and revolute, stems, stipules, peduncle, pedicels with hirsute indumentum, inflorescence a compound, 5-12 cm long, umbel, and by the pendulous, 8-11 mm long flowers.

Etymology
The specific epithet is based on the type locality, Mt. Hamiguitan, Davao Oriental, Philippines.

Distribution and habitat
This new species is currently known only from its type localities. Hedyotis hamiguitanensis occurs in the mossy forest of Mt. Hamiguitan at c. 1000 m elevation, and in pygmy forest on Mt. Hamiguitan at c. 1600 m elevation.

Phenology
Hedyotis hamiguitanensis was observed flowering and fruiting in April.

Provisional IUCN Conservation assessment
This species was only collected at the type localities. Although two populations were found, few individuals were observed in the mossy and pygmy forest. The distribution range of this species remains unknown. Thus, the conservation status of H. hamiguitanensis is Data Deficient (DD) based on the IUCN (2019)

Phylogenetic Analysis
The phylogenetic analysis (Fig. 3) based on the combined nuclear (ITS, ETS) and plastid (petD, rps16) data revealed that H. hamiguitanensis is embedded within the Hedyotis s str. clade (Neupane et al. 2015) and is sister to a clade consisting of H. schlechteri and H. valetoniana (BS=90, BPP=0.97), both from New Guinea. Although the two populations observed CB17051 and CB17036 showed differences in leaf size and thickness ( Figure  1A&B), phylogenetic analysis revealed that both populations formed a monophyletic group (BS=100, BPP=1.00), supporting the view that these two populations belong to the same species and the morphological differences may be due to adaptation to environmental conditions (Fig. 3).  dimensions, degree of curvature of the leaf blade margins, petiole length, inflorescence length, and flower size. The size differences of the two samples can be attributed to different environmental conditions -elevation, amount of sunlight and availability of nutrients in the soil.
Although the f lower orientation was not mentioned in the protologue descriptions of H.