By Jeanmaire Molina
The Philippines is a country of Southeast Asia, with its 7,107
islands strewn over the Western Pacific Ocean, approximately 13 N of
the equator and 122 E of Greenwich. Its collective land area is
about 300,000 sq. km, about the size of the state of Arizona. This
island archipelago is one of the most megadiverse countries in the
world, housing over 5% of the entire world’s flora in an area not
even 1% of the world’s total. An estimated 10,000 to 11,000 species
of plants are believed to occur in the Philippines and likely many
more if the tropical forests were fully explored and documented.
Over half of the named plants are endemic. This high level of
endemism is also present in the animals. Forty-four percent of its
vertebrate species and almost 70% of its insects are also found
nowhere else in the world (Catibog-Sinha and Heaney 2006). Among the
world’s 25 top biological hotspots the Philippines ranks second in
the number of species per square kilometer, thus the endemic species
are concentrated in exceptionally small areas (Myers et al. 2000).
Only 7% of its old growth closed-canopy forests remain from over 60%
in 1945 (Heaney et al. 2004). Therefore, these species are under
extremely high threats for extinction. As with any other developing
nation, poverty, overpopulation, ignorance, and political corruption
continue to threaten the remaining biological riches of this
With so many islands, the Philippines surpasses Hawaii and the
Galapagos in species biodiversity and endemism, and would be the
perfect system to understand why it is a cauldron of evolution. In
fact, the Philippines has been described as tenfold more diverse
than Galapagos (Heaney and Regalado 1998). As predicted by Wilson
and MacArthur’s (1967) theory of island biogeography, different
island sizes, ages and distance from mainland Asia have influenced
colonization, extinction, and diversification rates of Philippine
biota. These island features coupled with their individual
geological histories throughout the Cenozoic may hold the answer as
to why the Philippines is one of the world’s most biodiverse
Ancient geological history of the Philippine archipelago
As Australia drifted northward and began to collide with Asia,
tectonic pressure caused parts of the Pacific seafloor to uplift,
producing volcanoes that gave rise to the Philippine islands.
Sometime in the mid-Oligocene, about 30 mya, the Philippines was
starting to take shape with the development of three major
geological blocks (Fig. 1A). The first unit, which now comprise
modern day Palawan and Mindoro and other smaller islands, rifted
from the Asian continental shelf, south of the current location of
Taiwan. At about the same time, hundreds of kilometers southeast of
its present-day location, proto-Luzon, which began as a string of
small volcanic islands developing beneath a shallow sea, was moving
northwest. Further southeast of proto-Luzon, the islands of the
Visayas and Mindanao were borne out of the continued subduction of
the converging plates in the Pacific, and were also migrating
northwest. Throughout the Cenozoic, these major geological units
were approaching one another, but it was only in the Miocene that
they began to emerge above sea level (Fig. 1B). About 10 mya (Fig.
1C) Mindoro was uplifted and large land areas were already exposed
for the two other geological units. Starting in the Pliocene, 5 mya
(Fig. 1D), Palawan emerged, while other smaller islands and
peninsulas such as Bicol, Camiguin and Sibuyan, and the Sulu islands
only surfaced much later (Hall 1998; Heaney and Regalado 1998;
Steppan et al. 2003).
The 7000+ islands of the Philippines had never been connected to any
other Asian landmass, except for Palawan, which became contiguous
with Borneo when sea level dropped repeatedly during the
Pleistocene, accounting for Palawan’s biotic similarity to the
former. The isolation of the Philippines from the rest of Asia
allowed it to develop its unique flora and fauna, thus explaining
its staggering levels of endemism. Moreover, many species are not
only endemic to the Philippines but unique to individual Philippine
islands. Other islands, like Negros and Panay, share faunal species
which surprisingly are different from those on other adjacent
Visayan islands such as Leyte and Samar, whose fauna are, in turn,
more similar to those of Mindanao. Masbate’s fauna are also more
related to Negros and Panay’s than they are to the more proximal
Luzon. These patterns were observed in many vertebrates including
birds (Peterson et al. 2000), amphibians (Evans et al. 2003),
mammals (Heaney and Regalado 1998; Steppan et al 2003; Roberts 2006;
Esselstyn and Brown 2009), reptiles (McGuire & Heang 2001), and
fishes (Carpenter and Springer 2005).
Fig. 1. Postulated distribution of land and sea in Southeast Asia in
the Cenozoic. A. 30 mya. B. 20 mya. C. 10 mya. D. 5 mya. Figures
from Hall (2002).
Philippine Pleistocene Islands
Though the country’s ancient geology, beginning at least in the
Oligocene, had undoubtedly shaped Philippine biodiversity, biotic
similarities of certain island groups only make sense in the light
of the country’s Pleistocene history. About 2 mya, water evaporating
from the oceans formed very thick glaciers that blanketed temperate
regions for thousands of years, thereby resulting in global sea
levels 120 m below present. This allowed certain islands of the
Philippines to coalesce, forming Pleistocene island groups (Heaney
and Regalado 1998; Fig. 2), but after some time, the glaciers melted
thereby disconnecting these islands. This cycle went on repeatedly
several times with the last glacial episode culminating 12,000 yrs
ago and could explain the biogeographic patterns seen in many
Philippine vertebrate taxa (Catibog-Sinha and Heaney
During glacial events, five major Pleistocene island groups became
prominent: Greater Luzon (composed of Luzon, Catanduanes, Marinduque
and Polillo); Greater Mindanao (Mindanao, Bohol, Leyte, Samar,
Basilan); Greater Negros-Panay (Cebu, Masbate, Negros, Panay);
Greater Sulu (Tawi-Tawi, Sulu); and Greater Palawan. Except for
Palawan, these Pleistocene island groups have never been connected
to one another nor to the Asian mainland. The islands of Mindoro,
Sibuyan, Camiguin, and Siquijor have also remained isolated from any
other island (Heaney and Regalado 1998; Catibog-Sinha and Heaney
2006; Fig. 2). Thus, it is not surprising that each of these
Pleistocene islands harbors unique set of species. For example, 76%
of the non-flying mammals in Greater Luzon do not exist anywhere
else, and the number for Greater Mindanao is even higher at 79%
(Catibog-Sinha and Heaney 2006). Even the tiny, less than 500 sq. km
and solitary island of Sibuyan, has its own impressive array of
endemic species, in spite being only a few kilometers away from
It would seem reasonable to think that the recurring coalescence and
fragmentation of certain islands during the Pleistocene were
responsible for generating much of Philippine biodiversity, i.e. the
Pleistocene speciation hypothesis (Steppan et al. 2003). However,
this was not the case, at least for the species of a Philippine
endemic rodent, in which the timing of speciations occurred
pre-Pleistocene, during the Pliocene (Steppan et al 2003; Jansa et
al. 2006). The same story was reported for an endemic Philippine
fruit bat, whose genetically different populations resulted from
Pliocene diversifications (Roberts 2006). Nonetheless, for both
taxa, monophyletic groups are generally confined within the
boundaries of each Pleistocene island. This has led Heaney et al.
(2005) to conclude that distributional patterns of non-vagile mammal
species are generally consistent with the expectations of
Pleistocene geography, and that the latter may be predictive of the
biogeography of other species in oceanic archipelagoes.
However, not all Philippine species obey the Pleistocene geography
model and show complex diversification patterns; many even exemplify
cryptic speciations. For many Philippine bird species, allopatric
differentiations occurred after colonization of different islands
(Oliveros and Moyle 2010; Jones and Kennedy 2008). This was also
observed in Philippine shrews (Esselstyn et al. 2009) and skinks
(Siler et al. 2011). In their study of Philippine geckos, Siler et
al. (2010) were convinced that, though the Pleistocene geography
model has influenced terrestrial biodiversity patterns, it might be
an oversimplified paradigm, and that clade age, phylogenetic
diversification, ease of dispersal, and post-Pleistocene geography
may be invoked to explain vertebrate species diversity.
Philippine plant biogeography
But do the same biogeographic expectations hold for Philippine
plants? Do non-vagile species have distributions that reflect the
predictions of the Pleistocene model, while more easily-dispersed
species show more complex biogeographic patterns? Surprisingly, this
model has never been examined in Philippine plants. In fact, of the
74 references in ISI Web of Science that included the search terms
“Philippine biogeography”, only three were on plants (Tan 1996;
Linis 2009; Linis 2010). All three studies concerned mosses,
they were based soley on distribution data for individual Philippine
islands, and none of them used phylogenetic methods to test the
model. Biodiversity studies on Philippine plants are greatly
lacking. A complete flora for the country is lacking with the
checklist of Merrill dating to 1923. Botanical surveys for the
Philippines lag behind other comparable Malesian regions, with Java
and Peninsular Malaysia having at least 187 and 145 plant specimen
collections per 100 sq km, respectively, while the Philippinesis a
paltry 84 (Tan and Rojo 1989). Only <2% of the country’s flora
have also been evaluated by the International Union for Conservation
of Nature (IUCN; Catibog-Sinha and Heaney 2006). Even several
species of Rafflesia, the world’s largest flower, known to grow to
over 3 feet in diameter, have practically gone undetected in the
Philippines for the past 150 yrs, and it was only in the last decade
that 8 new species have been discovered, thus bringing the national
total to 10 (Barcelona et al. 2009, 2011). Incredibly, all but one
of these species are single-island endemics, and seem to follow the
Pleistocene model. A phylogenetic study of the group is
underway to confirm this.
We hope that through this website, we can motivate phylogenetic and
biogeographic studies on Philippine plants, to learn the mechanistic
processes of evolution in island archipelagoes, to understand how
ancient geology, Pleistocene geography, and tropical climate, acting
on a matrix of many islands of varying sizes, ages and proximities
have come together to produce a unique smorgasbord of species.
This work is urgent given that many of these species, sadly
teetering on the brink of extinction, exist in one of the world’s
most severely threatened biological hotspots.
Barcelona, J. F., P. B Pelser, D. S. Balete, and L. L. Co.
2009. Taxonomy, ecology, and conservation status of Philippine
Rafflesia (Rafflesiaceae). Blumea 54: 77-93.
Barcelona, J. F., E. S. Fernando D. L. Nickrent, D. S. Balete,
and P. B. Pelser. 2011. An amended description of Rafflesia
leonardi and a revised key to Philippine Rafflesia (Rafflesiaceae).
Phytotaxa 24: 11-18.
Carpenter, K.E. and V.G. Springer. 2005. The center of the center of
marine shore fish biodiversity: the Philippine Islands.
Environmental Biology of Fishes 72: 467–480.
Esselstyn, J.A. and R.M. Brown. 2009. The role of repeated sea-level
fluctuations in the generation of shrew (Soricidae: Crocidura)
diversity in the Philippine Archipelago. Molecular Phylogenetics and
Esselstyn, J.A. et al. 2009. Do geological or climatic processes
drive speciation in dynamic archipelagos? The tempo and mode of
diversification in Southeast Asian shrews. Evolution 63-10:
Evans, B.J. et al. 2003. Phylogenetics of fanged frogs: testing
biogeographical hypotheses at the interface of the asian and
Australian faunal zones. Systematic Biology 52:794–819.
Hall R. 1998. The plate tectonics of Cenozoic SE Asia and the
distribution of land and sea. In: Hall R and Holloway JD, eds.
Biogeography and Geological Evolution of South East Asia. Leiden:
Backhuys Publishers, 99–131.
Hall R. 2002. Cenozoic geological and plate tectonic evolution of SE
Asia and the SW Pacific: computer-based reconstructions and
animations. Journal of Asian Earth Sciences 20: 353–434.
Heaney, L.R. and J.C. Regalado, Jr. 1998. Vanishing Treasures of the
Philippine Rainforest. The Field Museum, Chicago.
Heaney, L.R. et al. 2004. Philippines. In R.A. Mittermeier, P.R.
Gil, M. Hoffman, J. Pilgrim, T. Brooks, C.G. Mittermeier, J.
Lamoreux, and G.A.B. da Fonseca (eds.), Hotspots Revisited: Earth’s
Biologically Richest and Most Endangered Terrestrial Ecoregions.
Mexico City: CEMEX.
Heaney, L.R. et al. 2005. The roles of geological history and
colonization abilities in genetic differentiation between mammalian
populations in the Philippine archipelago. Journal of Biogeography
Jansa, S.A. et al. 2006. The pattern and timing of diversification
of Philippine endemic rodents: evidence from mitochondrial and
nuclear gene sequences. Systematic Biology 55:73–88.
Jones, A.W. and R.S. Kennedy. 2008. Evolution in a tropical
archipelago: comparative phylogeography of Philippine fauna and
flora reveals complex patterns of colonization and diversification.
Biological Journal of the Linnean Society 95: 620–639.
Linis, V.C. 2009. Biogeography of Mindoro mosses. Blumea 54:
Linis, V.C. 2010. The moss flora of Camiguin Island, Philippines and
their floristic relations to some adjacent islands in the
archipelago. Telopea 12: 525–542.
MacArthur, R.H. and Wilson, E.O. 1967. The Theory of Island
Biogeography. Princeton, N.J.: Princeton University Press.
McGuire, J.A. and K.B. Heang. 2001. Phylogenetic systematics of
Southeast Asian flying lizards (Iguania: Agamidae: Draco) as
inferred from mitochondrial DNA sequence data. Biological Journal of
the Linnean Society 72: 203–229.
Myers, N. et al. 2000. Biodiversity hotspots for conservation
priorities. Nature 403: 853–858.
Oliveros, C.H. and R.G. Moyle. 2010. Origin and diversification of
Philippine bulbuls. Molecular Phylogenetics and Evolution 54:
Peterson, A.T. et al. 2000. Distribution of the birds of the
Philippines: biogeography and conservation priorities. Bird
Conservation International 10:149–167.
Roberts, T.E. 2006. Multiple levels of allopatric divergence in the
endemic Philippine fruit bat Haplonycteris fischeri (Pteropodidae).
Biological Journal of the Linnean Society 88: 329–349.
Siler, C.D. et al. 2010. Phylogeny and biogeography of Philippine
bent-toed geckos (Gekkonidae: Cyrtodactylus) contradict a prevailing
model of Pleistocene diversification. Molecular Phylogenetics and
Siler, C.D. et al. 2011. Phylogeny of Philippine slender skinks
(Scincidae: Brachymeles) reveals underestimated species diversity,
complex biogeographical relationships, and cryptic patterns of
lineage diversification. Molecular Phylogenetics and Evolution
Sinha, C.C. and L.R. Heaney. 2006. Philippine biodiversity:
Principles and Practice. Manila: Haribon Foundation Inc.
Steppan S.J. et al. 2003. Molecular phylogeny of the endemic
Philippine rodent Apomys (Muridae) and the dynamics of
diversification in an oceanic archipelago. Biological Journal of the
Linnean Society 80: 699–715.
Tan, B.C. 1996. Biogeography of Palawan mosses. Australian
Systematic Botany 9: 193–203
Recommended Citation: Pelser, P.B., J.F.
Barcelona & D.L. Nickrent (eds.). 2011 onwards. Co's
Digital Flora of the Philippines. www.philippineplants.org
Copyright © 2011, Co's Digital Flora
of the Philippines
Last updated October 21, 2012