Floristic Interchanges Between Formosa and the Philippines 
Hui-Lin Lii 
INTRODUCTION 
The floras of Formosa and the Philippines 
are, in spite of their geographic proximity, 
distinctive in their general nature. The two 
regions were separated by the Formosan rift 
(the Bashi Channel), probably in the early 
Tertiary, long before their connections with 
other respective neighboring areas were sev- 
ered. Thus the bulk of the Formosan flora was 
derived from China or from other floras that 
spread to Formosa through the Chinese main- 
land, while the bulk of the Philippine flora 
was derived from Malaysia and other lands 
south of the Asiatic continent. 
The distinctiveness of the two floras has 
been amply demonstrated by Merrill (1923). 
It will suffice to mention here the many tropi- 
cal and southern families that are present in 
the Philippines but absent from Formosa, 
such as the Dipterocarpaceae, Centrolepida- 
ceae, Monimiaceae, Nepenthaceae, Cunonia- 
ceae, Erythroxylaceae, Dichapetalaceae, Da- 
tiscaceae, Clethraceae, Epacridaceae, and Sal- 
vadoraceae. On the other hand, many other 
families, clearly of northern origin, occur in 
Formosa but are entirely absent from the 
Philippines, such as Cephalotaxaceae, Taxo- 
diaceae, Cupressaceae, Betulaceae, Lardiza- 
balaceae, Trochodendraceae, Papaveraceae, 
Geraniaceae, Callitrichaceae, Pyrolaceae, Dia- 
pensiaceae, Valerianaceae, and Dipsaceae. 
^ Research Associate, Morris Arboretum, University 
of Pennsylvania, Philadelphia. Manuscript received July 
1, 1952. The author is indebted to Dr. A. C. Smith of 
the Smithsonian Institution for his kindness in reading 
the manuscript and offering suggestions for its im- 
provement. 
However, though the basic constituents of 
the two floras are quite different, indicating 
their separate origins, their close geographic 
proximity allows certain floristic interchanges, 
apparently of relatively recent times. The dis- 
tance between the main islands, Formosa and 
Luzon, is about 350 kilometers. Stretching in 
the sea between the two is a chain of small 
islands, parts of the same volcanic line. The 
first group consists of three islands off the 
southeastern coast of Eormosa, Hoshaotao 
(Kotosho in Japanese), now called Lutao, 
Hungtauyu (Katosho in Japanese), now called 
Lanyu and commonly known as Botel Toba- 
go, and the tiny island. Little Botel Tobago. 
These islands are separated from the Batan 
(or Batanes or Bashi) Islands by the Bashi 
Channel at a distance of about 100 kilo- 
meters. The Batan Islands are separated from 
the Babuyan Islands, which are close to the 
northern coast of Luzon, by the Balintang 
Channel, about 70 kilometers wide. The dis- 
tance is nowhere great enough to make plant 
migration difficult. At South Cape, the south- 
ernmost tip of Eormosa, the small island 
Y’Ami of the Batan group, the northernmost 
of the Philippine Islands, is actually within 
sight. 
These small islands show remarkable affini- 
ties with the Philippine flora, even the north- 
ernmost ones, Lutao and Lanyu, which are 
closest to Eormosa. The conspicuous rela- 
tionship of the floras and faunas of the two 
latter islands to the Philippines has led some 
to suggest extending the Neo-Wallace Line 
northward from the Philippines, passing it 
between the main island of Formosa and these 
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