Small population with an estimated 200 mature individuals

Recently the presumed globally distributed Gyropous castaneus was separated into several phylogenetically and biogeographically restricted species of which one is the rare Gyroporus macnabbii from Australasia. The name is based on an Australian type collection from Queensland, but it remains to be proven (using sequence data) the New Zealand taxon is identical. The large separation distance and ectomcycorrhizal habitat strongly suggests the New Zealand population should be considered a distinct taxon. The analysis presented here is for the New Zealand occurrences only.

A distinct and uncommon species known from 5 verified records from 4 locations in upper half of North Island New Zealand. All locations under threat from land-use change, increased tourism, and invasive species, including Kauri die-back.

Preliminary category: Endangered. B2a populations <5, AOO <500km2, or Critically Endangered C1, or Endangered D1

Known from 5 verified records from 4 locations over a 53 year period in the upper half of North Island New Zealand. We infer the presence of 5 genotypes, x 8 to account for undetected colonies in under-recorded northern areas, x 5 to convert to an estimate of 200 mature individuals. Extent of Occurrence 530 km2, Area of Occupancy 16 km2

The species is ecotomyorhhizal with tea-tree (myrtaceae) and appears to restricted to tea-tree bush in the northern part of New Zealand. Many such areas are relatively under-recorded. This distinct species was not recorded for 48 years until re-discovered in 2018 in the Waikato.

The main populations are in the Waitakare Ranges west of Auckland where it has not been observed since the original records in the 1960/70s.  Of the 3 historic sites in this area 2 are now part of more recent housing developments. The remaining potential site is subject to increasing tourism with consequent impact on the immediate areas. The population is likely to decrease over the next 20 years as the impact of Kauri die-back on the dominant Kauri forest alters the forest structure. Areas are also likely to be disturbed because of disease management activity. The single remaining location in the Waikato region is in an area of tea-tree scrub adjacent to pasture. The impact of changing farming practice on adjacent areas is unknown