Systematics of the Philippine endemic Ixora L. (Rubiaceae, Ixoreae)

Ixora L. belonging to the tribe Ixoreae (Rubiaceae, subfamily Ixoroideae), is a large pantropical rain forest genus of shrubs and small trees. It comprises ca. 530 species that is presently subject to intensive investigations leading to far-reaching systematic changes. Recently, based on molecular evidence, Ixora was further enlarge to accommodate several genera (Captaincookia N.Hallé, Doricera Verdc., Hitoa Nadeaud, Myonima Comm. ex Juss., Thouarsiora Homolle ex Arénes and Versteegia Valeton). In consequence, tribe Ixoreae has become monogeneric. Although there have been a number of revisions focusing on specific geographical regions, e.g. in Africa, Madagascar, Marquesas Islands and Australia, the continental Asian taxa have never been fully revised and no clear picture of their diversity is available. In the Philippines, the only available account of Ixora is an enumeration by Merrill published in 1923 which is more than 85 years old and outdated due to numerous classification changes in the family Rubiaceae. To date, species diversity of Ixora in the Philippines remains poorly known and basic information on species distribution and ecology, taxonomic keys and diagnostic illustrations are limited. With this work, I want to fill a gap in our knowledge of the genus by assessing the phylogenetic relationships of Philippine representatives of Ixora: 1) using morphological and molecular data, 2) derive information on environmental requirements of Ixora species endemic to the Philippines using Maxent, and 3) publish a comprehensive taxonomic revision of the Philippine Ixora including nomenclatural treatments (lectotypifications) and new records, full illustrations, distribution maps and keys of the recognized taxa. An important first result of the present research was the finding that Philippine Ixora is polyphyletic, with representatives from at least three independent lineages. In both the parsimony and Bayesian analyses of the combined chloroplast markers (rps16 and trnT–F) and nuclear markers (ITS and ETS), two main lineages of Ixora were recovered, an Asian-Pacific lineage and an Asian-African-Malagasy-Mascarene-Neotropical lineage. Also, the results of the Statistical Dispersal-Vicariance Analysis (S-DIVA) revealed a complex biogeographical history for Ixora with several dispersal and vicariance events that have led to its current distribution. Furthermore, Philippines are shown to constitute an overlay zone into which species from both major lineages of Ixora, the Pacific and the African-Asian one, have immigrated and subsequently radiated. The results presented also revealed for the first time the bioclimatic relationships of endemic Philippine Ixora and showed that the species preferred areas with lower amount of annual rainfall and regions with higher annual precipitation variance (standard deviation). This may indicate the species’ potential to adapt to the changing climate or an adaptation of the species to monsoon seasons in the Philippines. This is of particular importance as it was reported that Philippines will experience a substantial difference in terms of seasonal rainfall change in most parts of the country due to climate change. Ecological niche modelling was carried out for the two species with most occurrence records, I. bartlingii and I. auriculata, using Maxent. Model results suggested that these two Ixora species will shift their geographic distributions under predicted levels of climate change. These models can be used to assist in designing conservation strategies for the species as it identified localities and areas with the potential to withstand climate change until at least 2080. Lastly, a taxonomic revision of the Philippine species of Ixora was done following the methods of classical herbarium taxonomy. A total of 31 species is recognized from the previously described 41 species; the remaining 10 species are recognized as synonyms of other well-defined species. Ixora mearnsii, I. pilosa and I. propinqua are considered as doubtful species, and are to be excluded. Additionally, three new species (I. alejandroi, I. reynaldoi, and I. silagoensis) are reported. Three more flowering specimens which may well represent additional new species but are not formally named because they are too imperfectly known are also included. A detailed morphological, anatomical and biological documentation of the recognized Philippine species of Ixora is given. All species are extensively described, native species illustrated and a taxonomic key to native and cultivated species is provided. Distribution maps with full citations of all specimens seen are supplied for each taxon.

Level thesis:degree_level

thesis.doctoral

Grantor dc:publisher

Universität Bayreuth

Year

2014

Author dc:creator

• Banag, Cecilia

Contributors dc:contributor

• Liede-Schumann, Sigrid

Repository record source_url

https://epub.uni-bayreuth.de/id/eprint/1837/

OAI identifier oai:identifier

oai:epub.uni-bayreuth.de:1837