Decaisninatomentosa (Loranthaceae), a new species of mistletoe from Samar Island, Philippines

Abstract Background The extensive forests over limestone of the Samar Island Natural Park (SINP) on Samar Island, Philippines harbour a rich variety of unique species. In this contribution, we describe and illustrate a new Loranthaceous mistletoe, endemic to Samar Island named Decaisninatomentosa, representing the 12th member of the genus reported to the Philippines. New information This new species is similar to D.confertiflora (Merr.) Barlow with respect to the presence of shortly and densely off-white tomentose inflorescence and 6-merous flowers. However, it is unique amongst congeners in having tomentose and partially fused bracteoles which cover almost or entirely the ovary of individual flowers in the triads. To date, D.tomentosa seems to be restricted to the SINP and is only known from a handful of individuals. More studies are needed to properly assess the demography, host range, conservation status and phylogenetic position of this distinctive species of mistletoe.


Introduction
The Samar Island Natural Park (SINP) in Samar Island, Philippines is one of the largest contiguous old-growth forests in the country, covering approximately 333,300 hectares of mostly lowland dipterocarp rainforest and forest over limestone (Mallari et al. 2001, UNDP [United Nations Development Programme] 2007, Taylor et al. 2015. Due to its unique geomorphological karstic features, forests over limestones are areas of great biological importance worldwide with high endemicity and unique assemblages of flora and fauna (Fernando et al. 2008, Struebig et al. 2009).
Recent botanical explorations of forest over limestone in the SINP revealed a mistletoe that did not fit with any of the currently-described species reported for the Philippines. A detailed examination of its morphological features placed it within Decaisnina Tiegh (1895: 435) by Tieghem (1895), a genus with over 25 species distributed from northern Australia to the Eastern Malay Archipelago (including Java, Celebes and the Philippines) and reaching the Marquesas (Barlow 1997, POWO 2021. Decaisnina are aerial hemi-parasitic shrubs within the Showy Mistletoe family (Santalales, Loranthaceae) (Barlow 1993, Barlow 1997, Tandang et al. 2021. Inflorescence of this family can be axillary or terminal, racemes, spikes or umbels (Huaxing and Gilbert 2003).

Materials and methods
We conducted a field survey at the SINP in June 2021 aiming to document the regional flora along the eco-trail. We observed five individuals of an undescribed Decaisnina species at the site and took photographs of their habit and other important features from fresh material. The holotype and isotype specimens were prepared from a single individual. The species description was constructed by combining observations of living structures studied at the type locality along with measurements of material preserved in alcohol made at the Institute of Biological Sciences, College of Art and Sciences, University of the Philippines Los Baños. Measurements of morphological traits and anatomical features from the alcohol-preserved tissue were done under a stereomicroscope using a ruler and a digital caliper (150 mm; #245111, Tactix, Shanghai, China). After studying the material, specimens were processed into vouchers following standard protocols. The holotype was deposited at the Philippine National Herbarium (PNH), while the isotype was deposited at the College of Agriculture Herbarium UP (CAHUP) (acronyms follow Thiers 2021). Morphological data from closely related species used for comparisons were obtained from published literature.
In spite of conducting three separate expeditions during the months of June, September and October (~ 20 days) to the SINP from Paranas to Taft,covering approximately 30 km of terrain searching for more populations of the undescribed Decaisnina, we could not locate more individuals. We acknowledge that the lack of additional individuals limits our ability to assess the range of morphological variation within this species. However, the key characters separating D. tomentosa from related taxa were present in all of the individuals observed, suggesting that these features are consistent and, thus, of taxonomic value. The recognition of this new species follows the morphological-phenetic species concept, which clusters entities sharing a series of morphological characters and separate them from others by consistent morphological gaps (Judd 2007). Given the current lack of genomic data for the new species, we are unable to test concepts on phylogenetic classifications, but future molecular studies should infer its evolutionary history to assess relationships and confirm its uniqueness from a phylogenetic perspective.

Diagnosis
Decaisnina tomentosa (Fig. 1) is similar to D. confertiflora (Merr.) Barlow with respect to the presence of shortly and densely off-white tomentose inflorescence and 6-merous flowers. However, the new species differs by its rounded ste, (vs. stem internode distinctly angular), cuneat leaf base (vs. truncate or slightly cordate at the leaf base) and corolla that is distinctly inflated teice (vs. slightly inflated at the base). Also, the new species has a longer corolla measuring 27.9-29.2 mm (vs. 16-20 mm). Highly distinct flowers that are subtended with a tomentose cup formed by the fusion of the bracteoles with slightly cucullate lobes and glabrous inside which almost or entirely cover the ovary of individual flowers, and corolla tomentose, double inflated at base and middle. We consider that the combination of these and other characters presented in Table 1 are significant for the recognition of this new species.

Etymology
The specific epithet "tomentosa" refers to the short soft indument densely covering the inflorescence of the new species.

Ecology
Regarding interactions with potential pollinators and seed dispersers, no floral visitors or fruit consumers were observed during our visit to the site. Given the morphological features of flowers and fruits, it is probable that they are pollinated and dispersed by birds. Systematic field observations and experimental studies are needed to assess pollinators and effective seed dispersers and to document interactions with other organisms. Table 1.  Barlow (1997).

Conservation
During the first field survey in June 2021, we observed a tree of Baccaurea philippinensis Merr. (1915: 275) (Phyllanthaceae) parasitised by five individuals of D. tomentosa. Searches for additional individuals in the area were unfruitful. Two additional explorations to the SINP in September and October 2021 failed to locate more individuals. Since D. tomentosa is only known from five individuals on a single tree, we believe that the species is vulnerable to extinction. However, we need information from additional surveys to identify more individuals and perform quantitative assessments on its demographic profile, current distribution, host range and potential threats. Therefore, we consider that the species should be listed as Data Deficient (DD) (IUCN Standards and Petitions Subcommittee 2019) until more field assessments are conducted to ascertain its actual conservation status.

Biology
Decaisnina tomentosa has been observed bearing flowers and fruits in the month of June.

Notes
Decaisnina tomentosa resembles the widespread species complex D. sumbawensis (Tiegh.) Barlow (1997: 304) due to morphological resemblances in the colour of the mature corolla (basally red and apically green), but the former can be separated from the latter by the presence of densely covered short soft hairs on the inflorescence (tomentose vs. puberulent).