Rediscovery of Botrychium boreale (Ophioglossaceae), a Fern Species Believed to be Extinct in Japan, with a New Record of B. lanceolatum on Mt. Usu in Hokkaido

Abstract

Populations of Botrychium boreale and B. lanceolatum were discovered on Mt. Usu, Hokkaido, Japan. In Japan, B. boreale, which is recognized as an extinct species, has only been recorded by a single population on Mt. Usu; however, its habitat was destroyed by the 1977 eruption of the volcano. Almost half a century later, we rediscovered a B. boreale population. Botrychium lanceolatum, which is a critically endangered species in Japan, has only been recorded on Mt. Rishiri and Hamatonbetsu-cho in Hokkaido, in addition to the subalpine areas of central Honshu. This newly identified population is the third locality of B. lanceolatum in Hokkaido, more than 400 km away from the closest known locality. Both populations consisted of very few individuals (< 20 in B. boreale and < 50 in B. lanceolatum), and the next eruption of Mt. Usu may be imminent, suggesting that conservation activities are needed immediately.