FLORA OF JAPAN 



INTRODUCTION 



In Europe and North America, many exhaustive floristic 

 works are available, but in our country the lack of such works 

 frequently has been keenly felt by us. Most of the early floristic 

 investigations on the Japanese flora, beginning in the 18th cen- 

 tury, were made by Europeans. Serious study and collecting by 

 Japanese botanists began first in the 1860's. The early published 

 works by our own botanists were mosdy regional floristic stud- 

 ies, although several floras of the entire Japanese archipelago 

 from time to rime have been published. One of the earliest was 

 that of Jinzo Matsumura, "Nippon shokubutsu mei-i," pub- 

 lished first in 1884, which went through nine editions. The 

 "Nippon shokubutsu-dzukan" ["Illustrated Flora of Japan"], 

 by Tomitaro Makino, first published in 1925, went through 

 several editions and reprints, the latest in 1963. The "Nippon- 

 shokubutsu-soran" ["Flora of Japan"], by Tomitaro Makino 

 and Kwanji Nemoto, first pubhshed in 1925, was issued the 

 same year as Makino's Illustrated Flora. The "Nova Flora 

 Japonica," by Takenoshin Nakai and M. Honda, 1935-51, un- 

 fortunately was never completed. 



The writing of my original Japanese edition began in 1947 

 after more than 30 years' study on our flora. The aim was to 

 produce a manual for botanists, dendrologists, foresters, and 

 agriculturists, and a guide book for students who require a 

 ready source of taxonomic information about the plants of 

 Japan. 



The present work enumerates all spontaneous plants inclu- 

 sive of the ferns and fern allies, gymnosperms, and phanero- 

 gams. Synoptical keys are included for all taxa to the level 

 of the species. A conservative interpretation of the taxa has 

 been attempted. In complex groups, such as Sasa, Aconitum, 

 Hosta, and others, where innumerable microspecies have been 

 recorded by specialists, it has not been possible to include these 

 in my Flora. Trivial variations in flower color, horticultural 

 variants, local aberrations in vegetative morphology, such as 

 dwarfs and monstrosities, are generally excluded. Exceptions 

 to this are in instances where garden plants, long known to us, 

 are enumerated as having originated from elements of our 

 indigenous flora. Wherever such garden plants appear, the 

 nomenclature is in accordance with modern usage in the nam- 

 ing of horticultural plants (International Code for Cultivated 

 Plants, 1961). A few plants of Chinese origin, long established 

 in our country, such as Mahonia japonica, Prunus japonica, 

 Gin\go biloba. Magnolia liliflora. Clematis florida, and some 

 others, are also included. 



The Engler and Prand system of classification, as outlined in 

 "Syllabus der Pflanzenfamilien," has been adopted for the 

 phanerogams, and Copeland's "Genera Filicum" as the guide 

 in the treatment of pteridophytes. The aim was to construct the 

 analytical keys on the basis of phylogeny, but this has not al- 

 ways been practical or possible. Purely artificial keys often have 

 been constructed for the convenience of the user. The diag- 

 noses of the taxa and the keys are based almost wholly on avail- 

 able herbarium specimens. 



The geographical areas covered in this flora include all of 

 present-day Japan, excluding the Tokara Islands. The Japanese 

 archipelago is divided into eight segments: Hokkaido (includ- 

 ing Rishiri and Rebun islands), northern Tohoku, Kanto, 

 central, Kinki, and western Chiigoku districts of Honshu, 

 Shikoku, and Kyushu, including the adjacent islands of Tane- 

 gashima and Yakushima as the southern boundary. 



I am deeply grateful to the late Dr. G. Koidzumi, my men- 

 tor, for his kind instructions over a long time and to many 

 others for their many valuable suggestions. Dr. Y. Satake, S. 

 Okuyama, and K. Hisauchi have rendered kind assistance to 

 the author in various ways ever since he became a staff member 

 of the National Science Museum. Dr. T. Koyama helped in 

 preparing the drawings, reading proof, and making indexes, 

 as well as in various other ways. In the preparation of accounts 

 of complex plant groups various monographic studies by spe- 

 cialists were very helpful. To all authors of tiiese works the 

 writer is greatly obligated. 



I wish to mention that the original Japanese edition of this 

 work was partially sponsored by a Publications Subsidy of the 

 Ministry of Education, for which support I am deeply grateful. 



PHYTOGEOGRAPHICAL RfiSUMfi 



Japan supports a very rich flora in proportion to its size, a 

 circumstance of historical importance in relation to Japan's 

 early closer relationship with mainland Asia and to its subse- 

 quent development as an insular province with highly distinc- 

 tive geographical characteristics. Historically, the Japanese 

 home islands were a part of the continental landmass of Asia, 

 at least down to the Quaternary Period. For this reason, our 

 flora is most closely related to the Chinese flora, especially to 

 plants of the mountains of China, where many species exist as 

 relicts or as remnants of the much older Tertiary floras. That 

 Japan was not greatly affected by Pleistocene glaciation is a 

 factor which favored the preservation of older floras that might 

 otherwise have vanished. Moreover, the approximately 850- 

 mile length of the land area of Japan, extending over nearly 15 

 degrees of latitude from about 30° to 45° N. from the sub- 

 tropical belt of the southern areas to the alpine summits of 

 numerous mountain peaks together with a complex moun- 

 tain system that covers nearly 70 percent of the total land mass, 

 are factors that determine the component elements of the flora. 



The close proximity of the sea produces an insular climate 

 over much of the country. The warm Japan Current or Black 

 Stream (Kuroshio) , as it flows from southwest to northeast 

 along the Pacific side of the archipelago, influences all southern 

 and southeastern areas, giving them a relatively high precipita- 

 tion and little or no frost in areas near the coast. In these south- 

 ern areas are found many plants which occur principally in 

 areas farther south. In the north, the cool Kurile {Oyashio) 

 Current has a pronounced cooling effect on the climate of 

 northern Honshu. Likewise, in our northern areas and on the 



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