1. 1) a) Shimizu, T. and Satomi, N. (1976) A Preliminary List of the Rare and Critical Vascular Plants of Japan (1). Kanazawa;
2. b) Shimizu, T. and Satomi, N. (1977) A Preliminary List of the Rare and Critical Vascular Plants of Japan (2). Kanazawa.
3. 2) Threatened Species Research Group (ed.) (1989) Red-list of Vascular Plants of Japan. World Wildlife Fund, Japan & Nature Conservation Society, Japan, Tokyo (in Japanese).
4. 3) IUCN (2001) IUCN Red List Categories and Criteria version 3.1. IUCN, Switzerland.
5. Spherophylon, the concept of life at a level higher than that of the individual