Disjunctive patterns of Malesian mosses 235 Noteworthy disjunctive patterns of Malesian mosses Benito C Tan Farlow Herbarium, HUH, Harvard University, 22 Divinity Avenue, Cambridge, MA 02138, USA Key words: Malesian mosses, disjunction, plate tectonics, dispersal Abstract ported by moss distribution patterns On the other hand, the distributions of moss taxa across A review of some noteworthy patterns of disjunction of the Makassar Strait support the concept of a Malesian moss distributions is presented Correlation with Wallacean region over Wallaces Line as a de- new information from the plate tectonic history of the marcation separating the Asiatic and Australa- Malesian region offers a new interpretation of the origin and sian floras Nonetheless, the filtering effect of migration of Malesian mosses Although long distance and chance dispersal remain important explanations for local this biogeographical barrier on the spore-pro- plant distribution patterns, it appears that the climatic and ducing mosses is not as dramatic as is the case vegetation changes in Malesia during the Cenozoic are two with seed plants (Tan, 1984, 1992; Hyvönen, important factors contributing to the present-day patterns of 1989) Additionally, some areas in Borneo and moss distribution in Malesia Palawan that harbour an aggregation of uncom- mon moss taxa sharing similar ecological prefer- ence and also the same pattern of distribution Introduction have been taken to be refugia of species belong- ing to the Tertiary moist and the Quaternary dry Since the distribution of many Malesian mosses forests (Meijer, 1982; Tan, 1996) is intimately tied to the rain forest habitat, the An appreciation of the importance of study of Malesian moss diversity and distribution Malesian moss biogeography can be better has become more urgent today because of the achieved with an overview of the composition increasing rate of destruction of rain forests and affinities of Malesian mosses, which total across the entire region The complex patterns c 330 genera and 1,755 species It is clear from of the distribution of mosses in the region is Table 1 that the majority of Malesian species of matched by the diverse composition of the mosses (c%60%) have evolved in situ during the Malesian moss taxa geological formation of the various island The impact and the biogeographical implica- groups, notably Borneo and New Guinea Taxa tion of the knowledge of moss distribution in of clearly Laurasian and Gondwanan origins are Malesia must not be underestimated Based on nearly equal in number With the recent refine- published information, the distribution of ments in the plate tectonic history of the Malesian mosses, like their seed plant counter- Malesian region (see Hamilton, 1979; Audley- parts, supports recognition of distinct eastern, Charles, 1987; Hall, 1996), a review of the re- western and southern floristic provinces gional patterns of moss distribution, especially (Steenis, 1950; Tan, 1984, 1992; Touw, 1992a, those of the disjunctive taxa, is both instructive 1992b) The proposed scenario of a Central and timely Several of these patterns can now be Malesian province (see Johns, 1995) in place of better explained by relating them to local plate the South Malesian province is not well sup- tectonic movements than by a long distance dis- Biogeography and Geological Evolution of SE Asia, pp 235-241 Edited by Robert Hall and Jeremy D Holloway © 1998 Backhuys Publishers, Leiden, The Netherlands 236 B% Tan Table 1 Phytogeographical groupings/affinities of Malesian can be easily overlooked mosses (330 genera and 1,755 species) Another noteworthy revelation shown by the distribution patterns of mosses is the relatively Cosmopolitan taxa 30% slow rate of speciation in many groups Studies N Hemisphere/Laurasia 40% of fossilized mosses dated from Palaeozoic, Pantropical 23% Mesozoic and the Tertiary, reveal a remarkable Palaeotropical 10% similarity between the ancient and extant moss Palaeotropical and Oceania 48% Tropical Asia (including Eastern Himalayas) floras supporting the alleged evolutionary con- and Oceania 52% servatism of the plant group (Frahm, 1994) Sri Lanka, S India, E Himalayas, Indochina, China, Many of the fossil specimens can be identified to Taiwan, Japan and Malesia 92% families and genera that still exist today (Miller, Indochina, China, Taiwan, Japan and W Malesia 22% 1984; Krassilov and Schuster, 1984; Ignatov, Malesia 229% Widespread 132% 1990) It is therefore not surprising that some W Malesia 64% patterns of moss disjunction parallel those seen E Malesia 19% in flowering plants and vertebrates at a higher S Malesia 14% taxonomic level Narrow Endemics (restricted to 1-2 islands) 309% W Malesia 113% E Malesia 157% S Malesia 39% Noteworthy disjunctive patterns Malesia and Oceania 40% S Hemisphere/Gondwana 45% Chameleion peguense (Besch ) Ellis & Eddy and Disjunctive 30% Horikawaea redfearnii B C Tan & P -J Lin Not Certain 30% These two taxa (Fig 1) represent the continental Asia and Philippine disjunction which was ear- lier called the Indochina-Philippines disjunction persal hypothesis This is especially true in the by Tan (1984) Members of this group (c 2 2% of bryogeographical interpretation of the floras be- the total Malesian species) are widespread in tween Luzon and Mindanao, and also between continental Asia, becoming rare in wet parts of the floras of North Borneo and Kalimantan Bor- archipelagic Malesia, and are often known only neo New geological evidence indicates an inde- from the Philippines (Luzon and Palawan, see pendent plate tectonic history for each of these Fig 1) Some extend southward to the Malay pe- areas ninsula, but they are absent from Borneo, A word of caution is necessary here In spite Sumatra and New Guinea A broader version of of the large amount of new taxonomic informa- this pattern is seen in Pogonatum microstomum tion on Malesian mosses published in the (Dozy & Molk ) Dozy & Molk (see Touw, present decade, the moss flora of some pivotal 1992b, p 149, Fig 2), with additional populations islands, such as Mindanao, Sulawesi and Halma- present also in Java and the Lesser Sunda Is- hera, remains insufficiently known at present to lands Together, they probably represent deni- make definitive conclusions It is probable that zens of monsoonal, semi-deciduous forest and some of the disjunction patterns outlined below savannah communities that had a broad range represent under-collection in intervening areas across tropical Asia during the Oligocene A good example to illustrate how improved tax- (Morley, 1991) and Pleistocene (Morley and onomy and new collections alter the distribu- Flenley, 1987; Heaney, 1991) The subsequent tional status of a species is found in Luisierella climatic changes, beginning in the Miocene, barbula (Schwaegr ) Steere This species was may have caused the fragmentation of the once long thought to be a neotropical taxon until two expansive, seasonally dry vegetation of SE Asia, collections from Java and New Caledonia, which and its replacement by ever-wet rainforest such were erroneously named as Didymodon brevi- as exists today in Borneo, Sumatra and New caulis (Hampe ex C Muell ) Fleisch , were cor- Guinea Consequently, mosses requiring seasonal rectly identified in 1977 (Touw, 1992a) To date, drought disappeared the species is known additionally from Japan, In the case of Horikawaea redfearnii, which China, Borneo, Sulawesi, Java, the Lesser Sunda is known only from the seasonally dry forests of Islands and New Caledonia Its presence in Asia Hainan and Palawan Islands (see Fig 1), the dis- is probably incompletely documented because junctive pattern might have been brought about the species is a tiny moss of disturbed sites and by the drifting of the North Palawan-Mindoro Disjunctive patterns of Malesian mosses 237 Fig1 Distributions of Chaemeleion peguense (after Ellis, 1992) and Horikawaea redfearnii showing the continental Asia- Philippines disjunction Arrow indicates the possible direction of dispersal terrane from the vicinity of South China toward migration along the Himalayan-Philippine its present position in the Philippines during the mountain track proposed by Steenis (1964) Its Oligocene-Miocene (Hall, 1996) Additional ex- presence on Mt Kinabalu in Borneo and high amples of a similar disjunction across the South mountains in Mindanao can be predicted China Sea are Sphagnum robinsonii Warnst (Indochina and northern Luzon) and S% luzonense Dawsonia superba Grev , Bescherellia elegant- Warnst (Indochina, Yunnan and Luzon) issima Duby, Mittenia plumula (Mitt ) Lindb , A superficially similar pattern of disjunction, Thuidium sparsum (Hook f & Wils ) Reichdt but attributable to a different ecological factor, is and Orthorrhynchium elegans (Hook f & Wils ) shown by Trachycladiella aurea (Mitt ) Menzel Reichdt The species is a moss of humid montane forest; its total range was mapped by Menzel and Bescherellia elegantissima Duby (Fig 3) and Schultze-Motel (1994, p 79, Fig 4) It is common Dawsonia superba Grev are two mosses that in the eastern Himalaya, scattered through the exhibit an Australasian/Oceania or South Mal- mountains of S China, Taiwan, southern Japan esia/Philippine disjunction Members of this and northern Luzon, and reappears in the group (about 4 5% of the total Malesian species) mountains of Sulawesi, Seram and W Java Its are mostly widespread in rain forests in Aus- present distribution appears to follow a hopping tralia, New Zealand and New Guinea, spreading 238 B% Tan Fig2 Distribution