Floristic Interchanges Between Formosa and the Philippines

Floristic Interchanges Between Formosa and the Philippines HUI-LIN LI I INTRODUCTION However, though the basicconstituents of the two floras are quite different, indicating THE FLORAS of Formosa and the Philippines their separate origins, their close geographic are, in spite of their geographic proximity, proximity allows certain floristic interchanges, distinctive in their general nature. The tw<? apparently of relatively recent times. The dis regions wereseparated by the Formosan rift tance between the main islands, Formosa and (the Bashi Channel), probably in the early Luzon , is about 350 kilometers. Stretching in Tertiary, long' before their connections with the sea between the two is a chain of small other respective neighboring areas were sev islands, parts of the same volcanic line. The ered. Thus the bulk of the Formosan flora was first group consists of three islands off the derived from China or from other floras that southeastern coast of Formosa, Hoshaotao spread to Formosa through the Chinese main (Kotosho in' J apanese), now called Lutao, land, while the bulk of the Philippine flora Hungtauyu (Katosho inJapanese), now called was derived from Mal aysia and other lands Lanyu and commonly known as Botel Toba south of the Asiatic continent. go, and the tiny island, Little Botel Tobago. The distinctiveness of the two floras has These islands are separated from the Baran been amply demonstrated by Merrill (1923). (or Batanes or Bashi) Islands by the Bashi It will suffice to mention here the many tropi Channel at a distance of about 100 kilo cal and southern families that are present in meters . The Baran Islands are separated from the Philippines but absent from Formosa, the Babuyan Islands, which are close to the such as the Dipterocarpaceae, Centrolepida northern coast of Luzon, by the 'Balintang ceae, Monimiaceae, Nepenthaceae, Cunonia Channel, about 70 kilometers wide. The dis ceae, Erythroxylaceae, Dichapetalaceae, Da tance is nowhere great enough to make plant tiscaceae, Clethraceae, Epacridaceae, and Sal migration difficult. At South Cape, the south vadoraceae. On the other hand, many other ernmost tip of Formosa, the small island families, clearly of northern origin, occur in Y'Arni of the Baran group, the northernmost Formosa but are entirely absent from the ' of the Philippine Islands, is actually within Philippines, such as Cephalotaxaceae, Taxo sight. diaceae, Cupressaceae, Betulaceae, Lardiza These small islands show remarkable affini balaceae, Trochodendraceae, Papaveraceae, ties with the Philippine flora, even the north Geraniaceae , Callitrichaceae, Pyrolaceae, .Dia ernmost ones, Lutao and Lanyu, which are pensiaceae, Valerianaceae, and Dipsaceae. closest to Formosa . The conspicuous rela tionship of the floras and faunas of the two 1 Research Associate, M orris Arboretum, Unive rsity of Pennsylvania, Philadelphia. Manuscript re cei ve ~l)ul y latter islands to the Philippines has led some 1 1952. The author is indebted to Dr. A. C. Smith of to suggest extending the Neo-Wallace Line the Smithsonian Institution for his kindness in reading northward from the Philippines, passing it the manuscript and offering sug gestions for its im provement. between the main island of Formosa and these 179 180 PACIFIC SCIENCE, Vol. VII, April, 1953 two small islands (Kano, 1931). However, it largely confined to medium and high altitudes has been shown that the southern tip of For in northern Luzon. Such characteristically mosa, commonly known as the Hunchuen northern or Asiatic elements, mostly common (Koshun) Peninsula, has a flora quite dis genera in the mountains of Formosa, such as tinct from that ofthe Formosan mainland but Lilium, Liriope, Saururas, Tbesium, A rmaria, very close to that of these two small islands, Sedam, Duetzia, Rosa, Skimmia, BlIXlIS, Pistacia, showing similarly. distinctive relationships Androsace, Hoppea, Salvia, Ellisiophylillm, Hemi with the Philippine flora. There is a marked phragma, Peracarpa, Aster, Solidago, Anisopap infiltration of austral elements from the Phi pllS, and Artemisia, occur nowhere in the Ma lippines to Formosa, particularly in the ex layan region outside ofnorthern Luzon (Mer treme southern part of the island and in these rill, 1923-26). It is. apparent that Formosa is t~o small islands (Li and Keng, 1950). an important route of migration of these Asiatic types to the regions in the south (Van ' SOUTHWARD MOVEMENT OF Steenis, 1946). TEMPERATE ELEMENTS We may picture that during the Pleistocene Before the inception of this northward mi or earlier, when the general temperature was gration of relatively recent occurrence, as will much lower than now, these montane species be discussed later, there occurred another ex would have inhabited lower elevations and pansion of floristic elements in the opposite thus had greater ranges. Their ranges might direction, that is, from Formosa to the Phi have been more or less continuous, extending lippines . These elements, in contrast to the from the Himalayasand western China through southern tropical elements, mostly ofthe low the mountains of southern China to Formosa lands, are cold-temperate in nature and lim and Luzon . Subsequent rising of tempera ited to montane or alpine regions. In Formosa, tures forced these plants to higher elevations because of the massive and lofty mountain until finally they occupied the present iso ranges which occupy most of the central por lated mountain regions suitable for their exist tion of the island, there developed an exten ence. Thus, species like Hemiphragma betero sive alpine-montane flora rich in number of phyllllm Wall. and Ellisiophylillm pinnatum species. These plants show distinctively close (Wall.) Makino now have widely disjunct relationships with those ofwestern China and ranges on the high mountains of Luzon, For the eastern Himalayas and also to some ex mosa, western China, and the eastern Hima tent with the montane flora ofJapan in the layas, etc. north. These Philippine plants of northern origins There are over 40 peaks in the Formosan are sometimes specifically or subspecifically mountain .systems that exceed 1,000 meters distinct from their congeners in Formosa, in height. The highest peak is Yu Shan, or while others may be specifically identical. Mt. Morrison, towering to a height of 1,950 That some of these show morphological dif meters, the highest of all eastern Asia. Such ferentiation indicates that their separation an extensive, high mountain chain permits the must have been for a considerable length 'of existence of an alpine flora that otherwise time. As such plants are now confined to exists only in the Himalayas, western China, isolated and distant mountain regions and as and other mountain regions far north of For there were drastic .changes in climate during mosa. the geologically recent past, such a south From Formosa, a large number of tem ward migration of the montane flora may be perate elements, mostly of mountain regions , considered largely a matter of the past, there extend southward to the Philippines. In the being little possibility that the same process Philippine Islands, these Asiatic elements are is goin g on extensively at the present. Floristic Interchanges- LI 181 NORTHWARD MOVEMENT OF . the coastal lowlands. Their wide ranges are TROPICAL ELEMENTS due apparently to their more aggressive na In contrast to the southward migration of ture and especially to their wider tolerance of these ternperate elements , the northwardmove temperature extremes. ment oftropical elements from the Philippines In the second group are species like Acacia to Formosa is limited practically to the low con/usa Merr., Ipomoea polymorpha R. & S., and lands and particularly to the southern ex Oreocnide trineruis Wedd., which occur widely treme of the island of Formosa. Favored by in the Philippines and extend also to Formosa, the gradual rising of temperature since the especially along the coasts and lowlands, from Pleistocene, these tropical, or southern, plants south to north. The number of such species that find their way to Formosa are able to with wide ranges in Formosa is few, indicating establish themselves there. the insignificance of such elements and pos Apparently many strand plants migrate by sibly also their recent and scattered arrival. the help of ocean currents. In the case of There are many more species common to Formosa, the main current is supplied by the the Philippines and Formosa but confined in Japan Stream from the south which passes the latter island to the southern part. These along the island chain connecting the Philip species are sometimes limited only to the pines and Formosa. This chain ofsmall islands southernmost tip of the island-the Hun also acts as a series of stepping stones for the chuen Peninsula and the small islands of Lu migration of plants, especially from south to tao and Lanyu. Such species as Illigera luzon north. This northward migration of plants is ensis Merr ., Scbizostacbyum diffttsttm Merr., also aided by wind . The prevalent monsoon GoniothalamttS amttyon Merr. , Aglaia elliptici during the summer and fall and the general folia Merr. , Maba bttxifolia Pers., Guettarda track of typhoons rampant in the eastern Paci speciosa 1., Morinda citrifolia 1., Pempbis acidula fic during this same period of the year are also Forst., etc., are often important elements in in a northeastern direction from the tropics, the local vegetation. That their occurrence is often leading from the Philippines to For often limited to the seashore and coastal areas mosa. in Formosa distinctly indicates that they are That these islands serve as an efficient mi relatively recent arrivals. gration route of the northward movement of The flora of the two small islands, Lutao southern plants can be demonstrated by the and lanyu, off the southeast coast of Formosa presence of the following floral elements in is much more intimately related to the south Formosa: (1) species of wide tropical distri ernmost .part of Formosa than is generally bution, (2) species common to the Philip understood (l i and Keng, 1950).

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