A new diminutive species of Schismatoglottis (Araceae) from Samar Island, Philippines

. Schismatoglottis minuta (Araceae) is described as a new species and illustrated based on accessions collected from Samar Island, Philippines. The new species, belonging to the Calyptrata clade sensu Hay and Yuzammi is distinct from previously reported taxa. Due to its habitat preferences and low (<100) estimated number of mature individuals, we recommend that this noteworthy species should be considered as critically


INTRODUCTION
The aroid genus Schismatoglottis Zoll.& Moritzi (1846: 83) comprises about 139 species distributed across the Malay Archipelago, with extensions towards the Pacific Islands (e.g., Vanatu), Indo-China, and tropical to subtropical China (Hay 1996;Hay and Yuzami 2000;Wong et al. 2016;Wong et al. 2018).The islands of the Philippines host about 9% of its diversity, with most species restricted to one or few islands (Wong et al. 2010;Pelser et al. 2011 onwards;Boyce et al. 2015).Schismatoglottis in Samar Island is represented by four species: S. calyptrata (Roxb.)Zoll.& Moritzi (1846:590), S. edanoi A. Hay (2000: 121), S. plurivenia Alderw. (1922: 209), and S. samarensis A. Hay (2000:143), of which two species (S. edanoi and S. samarensis) are endemic.Given the recent descriptions of many new species of Schismatoglottis from Borneo and the Malay Peninsula (Boyce and Wong 2015;Wong 2012;Wong et al. 2020;Wong and Boyce 2021;Wong et al. 2022), it is plausible that the diversity of this numerous genus has not been fully assessed in the Philippines, especially at remote biological hotspots such as Samar Island.
While exploring Samar Island Natural Park at Paranas, Samar Island, the second author photographed a Schismatoglottis whose morphological characteristics did not fully match with any of the currently known Philippines species.The most notable features were its remarkably diminutive habit of about 3-6 cm tall and 21 cm wide, the cordate base of its leaves, and the size, slender shape, sharp tip, and white color of its inflorescences.Examinations of vegetative and floral characters suggest that this taxon belongs to the Calyptrata informal species group (sensu Hay and Yuzammi, 2000), which is characterized by having a long and persistent leaf sheath fully attached to stems, deciduous spathe limb, minute sessile stigmas, and inflorescences bearing an appendix of sterile male flowers that demarcate the pistillate and staminate sections (Hay and Yuzammi, 2000).
Further expeditions in Samar Island located a second population between Can-avid and Taft, and examinations of herbarium specimens revealed a third one at Matuguinao.Given the unique combination of characters that do not fit within the variation reported from conspecifics in the Philippines and the centralized location of Samar Island at the eastern edge of the Philippine Archipelago (Figure 1), we consider that this taxon represents an undescribed member of Schismatoglottis.
Hence, here we propose considering it as a new species, which appears to be restricted to Samar Island.

MATERIALS AND METHODS
Fieldwork conducted in March 2016, between June and October 2021, and in October 2022 aimed to document the occurrence of native and introduced species to prepare an updated floristic account for the Samar province.
Initial taxonomic descriptions and photo-documentation of key plant structures from collected specimens were done in situ at the type locality.Type specimens were kept in a field press treated with denatured alcohol prior to being transported to the Systematics Laboratory at the Institute of Biological Sciences, College of Arts and Sciences, University of the Philippines Los Baños, where they were pressed and dried.Some ripe inflorescences were preserved in alcohol vials to conserve the delicate structures of flowers at anthesis.Living plants were collected and cultivated by the first author (M.D.D.A.) to further observe developmental stages of structures, especially inflorescences.Morphological and microscopic characters of fresh specimens were carefully examined using a stereomicroscope and a compound translucent microscope.Measurements of large structures were taken using a ruler and a digital caliper (Tactix: 150 mm).Images of structures were analyzed using the software ImageJ (version 1.53o).After examinations, specimens were dried and mounted into herbarium sheets using standard procedures.Scientific illustrations were based on photos taken in the field using a Nikon D3400 camera or from material preserved in spirit collections.The terminology used in the description section concords with the one used by Hay and Yuzammi (2000) for descriptions of Schismatoglottis species.The holotype specimen was deposited at the Philippine National Herbarium (PNH), while isotypes were sent to the College of Agriculture Herbarium at the University of the Philippines Los Baños (CAHUP) and to the Forest Herbarium and Wood Collection (LBC).Herbarium acronyms follow Thiers (2021).
Besides our bibliographic survey, we studied the Schismatoglottis collection at the University of the Philippines Los Baños (LBC), PNH, CAHUP, and CMUH herbaria to search for previous collections of the putative new species.We were not able to locate any voucher matching the combination of morphological characteristics defining S. minuta except at CAHUP, where we identified two vouchers from the Province of Western Samar collected by M. Price and B.F. Hernaez in July 1975.It is worthy to note that the species delimitation concept being applied here is based on phenetics, which assumes that all operational taxonomic units sharing a set of morphological characters form a cohesive evolutionary assemblage (De Queiroz 2007).Based on the consistency in the range of the morphological characters observed among all known localities of the species here described and the fact that they are phenetically distinguishable from other members of the genus reported for the Philippines, we assume that they represent an independent evolutionary lineage distinct enough to merit recognition as a new species.However, this hypothesis is open to debate when biological and phylogenetic data become available and we can resolve relationships within

Diagnosis
Schismatoglottis minuta can be distinguished from S. prietoi by its longer petioles 5-7 cm (vs 3-5 (-9) cm long); narrowly lanceolate to narrowly cordate or rarely cordate leaf outline (vs ovate to oblong-ovate to narrowly elliptic leaf outline); leaf apex acute (vs leaf apex acuminate); leaf base rounded with posterior lobes sometimes overlapping (vs leaf base cuneate); spathe white below the constriction and whitish green at the upper portion (vs lower spathe light green and white with orange tip above); and limb with one constriction (vs limb with two weak constrictions).

Etymology
The specific epithet "minuta" refers to the overall small habit of this new species when compared to conspecifics.

Phenology
Observed to bear flowers during the months of March, September, and October.

Distribution and Ecology
Schismatoglottis minuta is so far only known from Samar Island, Philippines.The species is currently known from three localities in Samar, at the "Samar Island Natural Park, Municipality of Paranas", "Canavid, Municipality of Taft", and "Municipality of Matuguinao".The sites are rocky habitats with moist substrate under tropical lowland evergreen rainforest dominated by towering dipterocarp trees.The species grows as a terrestrial herbaceous lithophyte on low vertical cliffs along creeks with shallow running water and on rock crevices under full shade in forests over limestone.

Conservation status
This new species, thus far, is found only at three fragmented localities.All sites contain clustered populations of less than 100 mature individuals in total, mainly in forested habitats (D.N.T., pers.obs.).Two of the known localities where S. minuta has been observed are not within the protected land (i.e.Can-avid and Matuguinao), and we expect that there will be a reduction in population size in more than ten years.Thus, following the IUCN Standards and Petitions Committee (2019), this noteworthy species is proposed to be categorized as critically endangered under criteria A4, B2a, C2a, and D1.

DISCUSSION
The addition of S. minuta raises to 13 total number of Schismatoglottis species reported for the Philippines (Pelser et al. 2011-onwards).Schismatoglottis minuta is one of the smallest species in the genus, especially if compared to the rest of congeners occurring in the Philippines (Hay and Yuzammi 2000;Boyce et al. 2015).The only two other Philippine species of Schismatoglottis with relatively small size are S. prietoi P.C.Boyce, Medecilo & S.Y.Wong (2015: 407) and S. mindanaoana Engler (1912: 103).The former occur in Cebu and Luzon, while the latter is endemic to Mindanao.Of these, the taxon with closest morphological resemblance is S. prietoi.
Despite sharing an overall miniature size, S. minuta and S. prietoi can be differentiated by the shape of their leaves (blades with cordate base vs cuneate base; Figures 2 and 3), inflorescences with staminate to female zones contiguous vs very short sterile interstice (Figure 3), and flowers with two stamens vs 3-4 stamens.Furthermore, S. minuta has a white urceolate-shaped spathe vs pale green to white cylindric.Additional characters separating both species include cross sections of their leaf petioles ("U" vs "D" shapes), number and angle of primary lateral veins (6-7 diverging at 40°-42° vs 3-5 diverging at 30°-60°), and diameter of floral stigma (0.1-0.2 vs 0.3 mm).
The shallow to deeply cordate leaf base shape of S. minuta appears to be consistent among individuals in the three sites where the species has been found (Figures 1 and 5).In fact, this is the most noticeable character to differentiate it from S. prietoi, all known populations have leaves with cuneate leaf and has not been reported for Samar Island.
The forests of Samar Island are highly diverse but have been poorly studied, as reflected by the many species of flowering plants described from there in recent years (e.g., Adorador et al. 2021;delos Angeles et al. 2022;Tandang et al. 2022).These high levels of endemism are mainly concentrated in forests over limestone, as discussed in Tolentino et al. (2020).Future field expeditions in highly threatened habitats outside protected areas should emphasize not only collections of voucher specimens, but also samples for genomic studies and germplasm for ex-situ conservation efforts in national and international botanic gardens.

Figure 2 .
Figure 2. Schismatoglottis minuta Tandang & M.D.Angeles-A.Humid habitat along river edges habitat B. Rocky habitat on crevices of Forests over limestone habitat C. Habit D. Leaf with non-overlapping posterior lobes (adaxial view) E. Leaf with non-overlapping posterior lobes (abaxial view) F. Leaf with overlapping posterior lobes (adaxial view) G. Leaf with overlapping posterior lobes (abaxial view) H. Petiole margin I. Cross section of petiole J. Leaf sheath of petiole showing incurved margins K. Viviparous plant emerging from the base a leaf blade L. Leaf margin (adaxial view) M. Leaf margin (abaxial view) N. Mature infl orescence O. Infl orescence with fl owers at staminate anthesis (spathe partially removed to show upper portion of spadix) P. Spadix (spathe artifi cially removed) Q. Unripe infructescence showing an enlarged spathe (Photo credits: D.N. Tandang: A; M.D. delos Angeles: B-Q).