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E.S. Femand~: Vegetation of the Philippine lslands 9
Despite its essentially Sundaic or West Malesian affinity the Philippine angiosperm flora is quite
distinct at the species level.
Origin and Geographical Relationships
The angiosperms are generally believed to have begun to evolve during the Lower Cretaceous
at about the time Gondwanic fragments started to drift northwards and became isolated.
From what is now known of the complex geological history of the Philippine archipelago and of
present plant distribution patterns, it is evident that the angiosperm flora of the islands have
originated in a variety of ways and from different sources. They are essentially of composite
origin, Laurasian or Asiatic and Gondwanic or AustralianIPapuasian. Thus, within the
archipelago there has been convergent migration and further evolution of the relict flora. The
long succession of extraordinary situations in the history of the islands may have contributed to
some sort of rapid speciation.
The floristic alliances of the Philippines are with Malesia. It clearly belongs to the area west of
Wallace's Line (West Malesia) together with Borneo, Malay Peninsula and Sumatra. At least
181 Asiatic- and West Malesiancentred genera find their eastern limits in the archipelago
(Steenis 1950).
The mainland Asiatic elements in the Philippine flora are often associated with vegetation
confined to medium and higher elevations. Steenis (1950) noted some 32 Asiatic-type genera
occurring in the archipelago. Of these 23 are found only on Luzon and 21 genera are montane
plants. At least 13 are not known elsewhere in West Malesia (Table 4). Many of these
mainland Asiaticcentred genera may have reached Luzon via the Formosa-Batanes-Babuyan
island arc. The continental fragment that rifted off South China and collided with the central
Philippines could have also served as a stepping stone for migration of Asiatic plants into the
archipelago (Tan et al. 1988).
Within West Malesia, the Philippine flora is closely allied with Borneo. About 66 species (Merrill
1926) and certain genera (e.9 Ludekia, W~lliamsia, Tetralopha, Myrmeconauclea in Rubiaceae,
Hallieracantha in Acanthaceae, and Philbomea in Linaceae) are restricted to Borneo and the
Philippines. In the Philippines, these genera mainly occur either in the Calamian-Palawan-
Balabac area or the Zamboanga-Basilan-Sulu-Tawi Tawi area: all areas lie more or less
geologically within the Sunda Shelf together with Borneo. Some species previously thought to
be Philippine endemics are now known to occur in Borneo. On the other hand, many Bornean
species have now also been recorded from Palawan (Hilleshog 1985).
The Australian-Papuasian or eastern element in the Philippine flora is also well-developed. In
fact, in West Malesia only the Philippine lslands have an appreciable eastern floristic element.
About 64 genera of Australasian affinity occur in the archipelago (Steenis 1985). Of these 18
are montane genera occurring above 1500 m alt. Some 30 eastern-centred genera occurring in
the Philippines are so far not known elsewhere in West Malesia (Table 5).