Three new species of Begonia sect. Baryandra from Panay Island, Philippines

Background The flora of Panay Island is under-collected compared with the other islands of the Philippines. In a joint expedition to the island, botanists from Taiwan and the Philippines found three unknown Begonia species and compared them with potentially allied species. Results The three species are clearly assignable to Begonia sect. Baryandra which is largely endemic to the Philippines. Studies of literature, herbarium specimens, and living plants support the recognition of the three new species: Begonia culasiensis, B. merrilliana, and B. sykakiengii. Somatic chromosomes at metaphase were determined to be 2n = 30 for B. culasiensis and 2n = 28 for both B. merrilliana and B. sykakiengii, congruent with those of most species in sect. Baryandra. Molecular phylogenetic evidence is consistent with B. culasiensis being a relict from the late Miocene and B. merrilliana and B. sykakiengii being younger species of Pleistocene origin. Conclusion The continuing discovery of endemic Philippine species means the remaining fragments of both primary and secondary native vegetation in the archipelago are of increasing value in terms of natural capital. A secure future for the species could be realized through ex situ conservation collections and raising awareness with community groups.


Background
In continuation of our taxonomic and evolutionary studies of Philippine Begonia (Nakamura et al. 2013;Rubite et al. 2013Rubite et al. , 2014Rubite et al. , 2015Hughes et al. 2015;Tandang et al. 2016;Peng et al. 2017), we document novelties of Begonia on Panay, the sixth largest island of the Philippine Archipelago. Elmer Merrill was the first to explore Begonia in Panay Island, describing six new species, B. collisiae Merr., B. lancilimba Merr., B. obtusifolia Merr., B. panayensis Merr., B. rubrifolia Merr., and B. serpens Merr. (Merrill 1919). There were no further reports on the begonias of Panay since then (Rubite and Madulid 2010). After securing the necessary permits, a joint expedition to Panay was  ) and previous phylogenetic placement .
literature, herbarium specimens, and flowering/fruiting plants cultivated in the experimental greenhouse, Biodiversity Research Center, Academia Sinica. The three new species were compared with the most closely allied members of sect. Baryandra. Begonia culasiensis was compared to B. rubrifolia;B. merrilliana to B. obtusifolia;and B. sykakiengii to B. nigritarum. Voucher specimens (B. culasiensis, Peng 23759;B. merrilliana, Peng 23765 and B. sykakiengii, Peng 24588) are deposited at PNH and HAST.

Chromosome preparation
Somatic chromosomes of B. culasiensis, B. merrilliana, and B. sykakiengii were examined using root tips from plants of the type collection. The methods of pretreatment, fixation and staining for chromosome observations followed Peng et al. (2015). Classification of the chromosome complements based on centromere position at mitotic metaphase follows Levan et al. (1964). Voucher specimens (Peng 23794, Peng 23765, Peng 23890) are deposited in HAST.

Species descriptions
Etymology: Named for its locality, the Municipality of Culasi, where the new species was discovered.
Provisional IUCN category: Following the Red List criteria of the IUCN (2012), we consider Begonia culasiensis to belong to the Vulnerable category under criterion D2 (population with a very restricted area of occupancy). Although there are several sub-populations along the forest trail in the Municipality of Culasi where the species was discovered, heavy use of this trail has led to an observed decline in numbers between visits by one of the authors in 2006 and 2012.

Begonia sykakiengii Rubite, C.I Peng, C.W.Lin & K.F.Chung, sp. nov. (
Distribution and ecology: Begonia sykakiengii is endemic to the Municipality of Maayon. On vertical cliffs face of exposed or semi-exposed limestone hills, at ca. 0-50 m in elevation.
Etymology: Mr. Sy Ka Kieng, patriarch of a Chinese family who has supported R. Rubite's field trips.
Provisional IUCN category: Following the Red List criteria of the IUCN (2012), we consider Begonia sykakiengii to belong to the Endangered category under criteria B2ab(iii) [(a) severely fragmented or known to exist at no more than five locations; (biii) continuing observed decline in quality of habitat). This species is a microendemic, restricted to a single cave which is not in a formally protected area. The site is surrounded by rice fields and habitation, and graffiti at the cave entrance indicates the site is already disturbed.

Chromosome cytology
Philippine species of Begonia formerly placed in sect. Diploclinium were transferred to sect. Baryandra based on molecular evidence ). Among 48 species recognized in sect. Baryandra, chromosome numbers of ten species were previously reported:  Rubite et al. 2015). In our study, 2n = 30 was determined for B. culasiensis (Fig. 9a), and 2n = 28 was determined for B. merrilliana and B. sykakiengii (Fig. 9b, c, respectively). Our data are congruent with those of most species in sect. Baryandra for which chromosome numbers are known.

Molecular phylogenetics
Begonia culasiensis represents one of the earliest branching lineages in Begonia sect. Baryandra (Fig. 10), and likely represents a relict lineage which has been present on the island of Panay since the Miocene . Begonia sykakiengii and B. merrilliana belong to the same clade as each other, highly nested within Begonia sect. Baryandra and of Pleistocene origin, and represent part of an endemic radiation on Panay. Two populations of Begonia culasiensis and B. sykakiengii were sampled in the phylogeny, showing some chloroplast sequence diversity to be present between populations of the species.

Discussion
Of the 25 conservation priority biodiversity hotspots identified by Myers et al. (2000), the Philippines has the lowest percentage of remaining primary vegetation, at 3%. Hence the continuing discovery of endemic Philippine species means the remaining fragments of both primary and secondary native vegetation are of increasing value in terms of natural capital for the Philippines.  The molecular phylogenetic results show a relict endemic element to the Begonia flora of Panay . Given the complex geological history of the island, which includes fragments of the Palawan microcontinental block (Hall 2002), further studies on different groups with an endemic element on Panay would be useful, as it is potentially a key area in the geological and biotic evolution of the archipelago.

Conclusions
The discovery of three new species endemic to Panay highlights the importance of the island to the Philippines in conservation terms. The next step is to ensure the long-term future of the species described here in both ex situ collections in their native localities. This is an opportunity for botanic gardens and community conservation groups in the Philippines to achieve a high impact at low cost, as the species are relatively easily cultivated, and have small native populations which could potentially be protected in micro-reserves (Appendix).