Assessment Notes

Justification

This species has a small population size estimated as up to 1500 mature individuals, all in a single subpopulation, which is continuing to decline due to decreasing extent and quality of its habitat. It therefore qualifies as Endangered C2a(ii).

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Taxonomic notes

Russula pleurogena is a small brown species, recognised because of its eccentric stem and habitat. The genus has been extensively surveyed and studied in New Zealand over a period of 60 years and this species not re-found since the original collection in 1981.

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Geographic range

The only known collection of this species is from Waitakere Ranges, near Auckland, New Zealand.

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Population and Trends

It has only been recorded once, from a single site. Considering that a number of other related species are restricted to northern North Island, it is reasonable to suppose that this one is similarly restricted. Taking into account the distribution of this habitat, 100 sites is thought to be a likely maximum to account for sites at which it is so far unrecorded. We infer the presence of 3 genotypes per site each representing 5 mature individuals, to convert to an estimate of 1500 mature individuals, all within one subpopulation.

Given the historic extent of the host we infer a decrease of at least 20% of suitable habitat (area and quality) during the last 50 years, which is causing a continuing decline in population size.

Population Trend: decreasing

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Habitat and Ecology

Russula pleurogena is ectomycorrhizal with tea-tree (Myrtaceae). The only collection had fruitbodies on stems of tree-fern and rotting wood, which is unusual for species of Russula.

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Threats

The original record dates from 1981 and subsequent surveys of the area have not relocated the species. The location is in an area subject to increasing tourism from the nearby Auckland city with consequent increase in disturbance in the immediate areas. The quality of the habitat in this area is also likely to decrease over the next 20 years as the impact of Kauri die-back on the Kauri forest alters the surrounding forest structure. Areas may also be disturbed because of future disease management actions, although the type locality is not currently affected.

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Conservation Actions

As this species has not been recorded since 1981, the most important initial action is to relocate it.

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Use and Trade

This species is not utilised.

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Source and Citation

Cooper, J.A. 2019. Russula pleurogena. The IUCN Red List of Threatened Species 2019: e.T154292955A154293720. https://dx.doi.org/10.2305/IUCN.UK.2019-3.RLTS.T154292955A154293720.en .Downloaded on 31 January 2021

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• Country occurrence