Ixora (Rubiaceae) on the Philippines - crossroad or cradle?

Abstract

BackgroundThe Philippine archipelago is globally one of the most important model island systems for studying evolutionary processes. However, most plant species on this archipelago have not yet been studied in sufficient detail. The main aim of this study is to unravel the evolutionary history and biogeographic relationships of the Philippine members of the pantropical genus Ixora.ResultsThe complex plastid and nuclear divergence patterns in Philippine Ixora, documented using tree and network approaches, reveal a highly dynamic evolution in Ixora, involving several phases of radiation and recolonization. Philippine Ixora comprises at least five lineages, of which one is most closely related to species from Wallacea, and the remaining four to species from Asia.ConclusionsOur study highlights the importance of Philippine species for understanding phytogeographic patterns in the Indomalayan-Australasian eco-region. The overall genetic differentiation, as well as the incongruence between genealogies based on the biparentally inherited nucleome and the maternally inherited plastome in Ixora, reflect the complex tectonic history of the Philippine archipelago. The Ixora lineage related to Wallacean species supports the delimitation of different ecozones along Huxley’s line, because it is absent from Palawan. The remaining four lineages are all allied with Asian taxa, reflecting several waves of colonization. Close relationships between some widespread Philippine species and locally adapted narrow endemics suggest that the widespread, genetically diverse species act as pools for the formation of new species in a process of ongoing speciation. Our results suggest that the species concepts of some of the more widespread taxa need to be revised.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-017-0974-3) contains supplementary material, which is available to authorized users.

A checklist of Rubiaceae species from Eastern Samar, Visayas, Philippines

“…The pantropical Ixora L. constitutes one of the largest Rubiaceae genus in the Philippines comprising of 34 species of woody shrubs and trees, with 25 endemic species (Banag et al 2015(Banag et al , 2017. Almost all Ixora have narrow ecological tolerances and are restricted to rainforest habitats (De Block 1998), as we observed.…”

Short Communication: Rediscovery of Psychotria species, subspecies, and varieties collected in the 1990s and new records of Antirhea benguetensis (Elmer) Valeton and Ixora longifolia Smith (Rubiaceae) in Northern Sierra Madre Natural Park, Luzon, Philipp

“…This study also reveals the discovery of Antirhea benguetensis (Elmer) Valeton, endemic, and Ixora longifolia Smith, non-endemic. Although the latter is not endemic in the Philippines (Banag et al 2017), it still deserves our sense of stewardship for its conservation. Botanical records proved that these species are not previously known in this national park.…”

Inventory of Rubiaceae species in Mt. Pao Range, Ilocos Norte, Northwestern Luzon, Philippines

“…Four species from the genus Ixora L. under the tribe Ixoreaea were collected, three of which are endemic, I. bibracteata Elmer (Figure 6.A), I. cumingiana S. Vidal and I. luzoniensis Merr (Figure 6.B). In the Philippines, out of the 34 species present, 25 are considered endemic (Banag et al 2015(Banag et al , 2017. The I. bibracteata are found along the trail and forest ridges at a medium elevation from ca.…”

“…In the past decade, there is an emergence of taxonomic and phylogenetic papers focused on the Philippine Rubiaceae (e.g.) Uy and Alejandro 2012;Obico and Alejandro 2013;Banag and Alejandro 2014;Villanueva et al 2016;Banag et al 2017;Chavez et al 2021;Ordas et al 2021). In addition, the recollection and discovery of new species Salamanes et al 2015;Alejandro and Meve 2016;Arriola et al 2016;Ordas et al 2017;Alfeche et al 2020;Biag and Alejandro 2020;Batuyong et al 2021b).…”