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Hidakasanmyaku Erimo Tokachi NP, Hokkaido
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Hidakasō grows in soil made from peridotite, a rock from Earth’s upper mantle. Its magnesium- and nickel-rich soil is thin, dry, and poor in nutrients—conditions that help keep forests at bay and shape this flower’s rare habitat.
At only 810 meters, nearby Mt. Apoi supports about 80 alpine-plant species, including nearly 20 endemic species and varieties. Summer sea fog, scant winter snow, and strong winds create conditions more like a much higher mountain.
Hidakasō flowers before its leaves unfold. Its overwintering buds sit close to the ground, and research found that spring ground temperature helps set its flowering time once the soil begins to thaw.
Local school principal and plant collector Tsushima Masao gathered the specimens that revealed this flower. It was once called Tsushima-sō; its adopted name, Hidaka-sō, honors the wider Hidaka region.
Using historical weather records and a temperature model, researchers estimated that Hidakasō began flowering about 7 days earlier than a century before. This is a model-based estimate, not a century of direct flower counts.
A 2025 presentation by Hokkaido researchers reported about 200 flowering Hidakasō in 2004, but only about 10–20 flowering individuals per year from 2020 onward. Field transplant trials began in 2025.
Heavy illegal collecting in the 1990s prompted local residents to form the Apoi-dake Fan Club in 1997. Members patrol for poaching, teach children about rare plants, and maintain trails to help prevent trampling.
Hidakasō habitat protection areas cover parts of both Mt. Apoi and Mt. Horoman. At Apoi, entry is banned away from the trail; the entire Horoman protection area is closed to entry.
In 1952, Mt. Apoi’s alpine plant community was designated a Special Natural Monument of Japan. Hidakasō is one member of this remarkable community—not the sole subject of the designation.
