Assessment Notes

Justification

Rhizopogon yakushimensis is an endemic hypogeous ectomycorrhizal fungus confined to and associated with Amami Pine (Pinus amamiana) that only grows on two islands in Japan. Amami Pine is globally Red Listed as Endangered and estimated to consist of about 2,300 trees. Although exploitation of the tree has ceased, infestations with pine wood nematodes continue to cause serious population decline. The status and trend for the population of Amami Pine set that for R. yakushimensis. Hence, R, yakushimensis is assessed as Endangered (EN) based on the restricted geographic range together with few locations.

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Geographic range

Rhizopogon yakushimensis is an endemic truffle obligately associated with the rare Amami Pine confined to Yakushima and Tanegashima islands in Kagoshima Prefecture, Japan. Using the latest Red List guidance, the extent of occurrence is estimated to be c.1,300 km², with an area of occupancy (AOO) estimated at 148 km². This is likely to be an overestimate for the AOO, though as it is unlikely to occupy the entirety of the mapped range.

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Population and Trends

Rhizopogon yakushimensis is confined to the distribution of Pinus amamiana. The population of P. amamiana approximately consists of 2,300 trees; 2,000 on Yakushima and 300 at Tanegashima (Katsuki and Farjon 2013). The exploitation of the tree has ceased, but infestations with pine nematodes continue to cause serious population declines (Katsuki and Farjon 2013). The population size of R. yakushimensis is estimated to be in the same range, or more likely, smaller than that of P. amamiana and to have the same population trend, i.e., declining. A study of mycorrhizal roots and the spore bank in the remaining four stands of Amami Pine revealed R. yakushimensis to be present and one of the dominating species in all stands (Murata et al. 2017).

Population Trend: Decreasing

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Habitat and Ecology

Rhizopogon yakushimensis is a hypogeous ectomycorrhizal fungus obligately associated with the Amami Pine, Pinus amamiana. Based on molecular phylogenetic characteristics and poor compatibility to form mycorrhiza with other pine species, it is considered that R. yakushimensis may be solely associated with P. amamiana on Yakushima and Tanegashima Islands (Sugiyama et al. 2019). An analysis of mycorrhizal roots and the spore bank showed R. yakushimensis to be present and among the dominant ectomycorrhizal fungi in all four stands with P. amamiana (Murata et al. 2017).

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Threats

The threats to Rhizopogon yakushimensis are the same as for the endangered tree Pinus amamiana. Pinus amamiana is globally Red Listed as Endangered (EN) as it is a rare and declining species, with a restricted range, the total population size amounts to fewer than 3,000 trees (ca. 2,000 on Yakushima) and is declining (Katsuki and Farjon 2013). These trees were formerly exploited for timber, and regeneration is slow probably due to inbreeding depression. Pine wood nematodes, Bursaphelenchus xylophilus, accidentally introduced from North America, have caused increased mortality on Tanegashima island (Tetsukazu Yahara pers. comm.).

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Conservation Actions

A few stands with Pinus amamiana in Yakushima and Tanegashima are protected, and actions are ongoing with the aim of conserving P. amamiana. This also benefits the conservation of Rhizopogon yakushimensis. A study analysing the presence of mycorrhizal fungi in the soil of P. amamiana subpopulations established ex situ on Yakushima island could not detect any R. yakushimensis (Sugiyama et al. 2019).

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Use and Trade

There is no use or trade of this species.

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Source and Citation

Murata, M. & Nara, K. 2022. Rhizopogon yakushimensis. The IUCN Red List of Threatened Species 2022: e.T217153181A217153186. Accessed on 23 November 2025.

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• Country occurrence