Study
Coarse-scale population structure of pathogenic Armillaria species in a mixed-conifer forest in the Blue Mountains of northeast Oregon
Ferguson, B. A.; Dreisbach, T. A.; Parks, C. G.; Filip, G. M.; Schmitt, C. L.
Canadian Journal of Forest Research, 2003
Armillaria was isolated from infected trees across a large area of mixed-conifer forest, and isolates were tested against one another for genetic identity, so that the boundaries of individual genetic individuals could be mapped.
- Studied in
- Armillaria ostoyae
- Sample size
- fungal isolates sampled across a mapped forest area
One genetically continuous individual of Armillaria ostoyae extended across roughly 965 hectares — about 9.65 square kilometres. Its age was estimated at somewhere between 1,900 and 8,650 years from the rate at which the fungus spreads through soil.
What it means
The authors' reading, and ours. Where they differ, that difference is the point.
How the authors put it
Individual Armillaria genets can occupy very large contiguous areas, with implications for how root disease is managed in these forests.
How NatureHQ reads it
The record behind "the largest organism on Earth is a fungus", and it repays reading closely. What was measured is genetic identity across an area, which is solid. What is inferred is that the area constitutes one organism, which depends on a definition — the mycelium may not be physically continuous everywhere, and a genetically identical, physically separated network raises the same question as an aspen clone or a strawberry runner. The age estimate is an extrapolation from spread rate, not a count of anything. NatureHQ presents the definition problem as the interesting part rather than as a technicality.
- Genetic identity across an area does not establish physical continuity of the mycelium throughout it.
- Age is extrapolated from an assumed spread rate over millennia.
- Sampling is necessarily sparse relative to the area claimed.
Walking a forest to find the edges of one fungus
How large can a single fungal individual be?
What this study is used for on NatureHQ
One study can inform several subjects. Here is everywhere this one is cited.
Published by: Canadian Science PublishingPublished in a Canadian Science Publishing journal.
This reference was resolved automatically against Crossref on 2026-08-30.
NatureHQ summarises research in its own words and does not reproduce published text. Reviewed 2026-08-30.