About a 20-minute walk from Palaceside Building in Takebashi, Tokyo, Chidorigafuchi and its surroundings still hold precious nature; I introduced Heike fireflies here the day before yesterday, but there is also a nationally designated natural monument. A natural monument in the heart of the city? Yet hikarigoke moss grows wild between the stone walls of Edo Castle ruins. Found by neighbors in 1969 (Showa 44), it was designated in 1972 (Showa 47) as extremely rare in the city center.
Hikarigoke appears to glow emerald in dark caves and the like, but it does not emit light on its own; spherical lens-like cells of the prothallus formed when spores germinate reflect faint light so it seems to shine in dark places
. It is sensitive to environmental change and dies from even slight shifts. It is classified in the Environment Ministry Red Data Book as Class IB — "high risk of extinction in the wild in the near future."
In Japan it ranges from Hokkaido to central Honshu and north; most sites are in national parks. Besides Chidorigafuchi's stone walls, three wild sites are designated: Iwadura, Saku City, Nagano Prefecture, and Yoshimi Hyakuana, Yoshimi Town, Saitama Prefecture.
According to the Ministry's Outer Gardens Office, which manages Chidorigafuchi, it is completely unknown whether hikarigoke came on large stones brought for the castle walls during Edo Castle construction, whether spores arrived from somewhere and grew between the stones, or when it first appeared. The recently published "Chidorigafuchi Environmental Restoration Plan," however, states, "We will protect organisms that have lived with historic sites such as stone walls, together with the environment." This hikarigoke is not yet strong or abundant enough for general public viewing, but if nurtured well it could become a draw.
Hearing "around the Imperial Palace," "stone," and "moss," one might think of the final phrase of "Kimigayo" and imagine hikarigoke as the moss "until pebbles become boulders" — but that seems unrelated. Still, hikarigoke and Heike fireflies — precious "glowing nature" rarely seen elsewhere survives around the Imperial Palace.