12 DERIVATION OF THE FLORA OF HAWAII 



Oahu and Kauai, and also on the windward side of Haleakala, on Maui, 

 at an elevation of about 4,000 feet. 



Probably the most conspicuous and one of the commonest liverworts 

 is Dumortiera trichocephala, a species widespread throughout the Indo- 

 Malayan region, but which does not occur in the American tropics, where 

 it is replaced by the cosmopolitan D. hirsuta, also occurring in Hawaii. 

 The Hawaiian specimens of D. trichocephala differ in some respects from 

 East Indian material from various localities, examined by the writer ; but 

 the differences are probably not of specific value. It occurs at lower 

 levels in Hawaii than is usual in the Malayan region, probably due to the 

 cooler climate of Hawaii. 



Often associated with Dumortiera is another large and conspicuous 

 liverwort, Wiesnerella denudata. This is a monotypic species, which at 

 present is known from only three other localities, viz., Java, the Hima- 

 layas and Japan. 



Both of these characteristic Asiatic species inhabit very moist, shady 

 localities, often on dripping cliffs or rocks along water courses, and they 

 would not seem to be well adapted to dispersal over wide areas of land, 

 let alone such expanses of ocean as lie between Hawaii and the Southern 

 Pacific. 



Quite as significant, perhaps, is the occurrence of certain so-called 

 "horned liverworts" (Anthocerotaceae). Two of these, Megaceros and 

 Dendroceros, are inhabitants of the rain forest. The latter was collected 

 only at elevations of about 4,000 feet, where the rainfall was almost in- 

 cessant. It is an epiphytic plant of extreme delicacy, and its thin-walled 

 green spores germinate immediately on ripening, and are quite unfitted 

 to survive even short exposure to the heat and dryness of the lowlands. 

 Megaceros is a larger and more robust plant, but is always confined to 

 moist and shady localities. Like Dendroceros, the delicate green spores 

 germinate immediately, and seem quite unfitted for transportation by 

 wind over any considerable distances, and the same may be said of the 

 majority of the liverworts of the higher rain forest. 10 The common 

 species of Megaceros is very similar to a species widespread through the 

 Malayan region. 



Stephani's Index Hepaticarum 11 shows that aside from the endemic 

 and cosmopolitan species, the Hawaiian liverworts are almost exclusively 

 species occurring in Southern Polynesia, Australasia, or Indo-Malaysia, 

 as there are only two American species which do not also belong to this 

 Old World. 



10 Campbell, D. H. : "On the Distribution of the Hepaticae," New Phytologist, 

 14,203-212. 1907. 



11 Stephani, F. : "Index Hepaticarum," Bull, de I'Herbier Boissier. 1898-1908. 



