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Geoglossum cookeanum Nannf.

Phylum: Ascomycota - Class: Leotiomycetes - Order: Helotiales - Family: geoglossaceae

Geoglossum cookeanum, France

Sometimes mistakenly recorded as Dead Man’s Fingers, Xylaria polymorpha, this earthtongue has some even closer lookalikes, including Trichoglossum hirsutum, Hairy Earthtongue. (The stem of the latter is minutely hirsute, but in other macroscopic characters it matches closely the description of Geoglossum cookeanum.)

This fairly common earthtongue fungus is found mainly in mossy, sandy grassland, often in dune slacks or on the edges of coastal pine forests.

Geoglossum cookeanum on a roadside verge in France

Distribution

Only occasionally recorded in Britain (including England, Wales and Scotland) and Ireland, Geoglossum cookeanum occurs also in several countries on mainland Europe including southwest France, where the main pictures shown on this page were taken.This earthtongue species is also reported to occur in some parts of North America.

Geoglossum cookeanum, southern England

Taxonomic history

This sombre earthtongue species was described in 1942 by Swedish botanist and mycologist John Axel Nannfeldt (1904 - 1985), who gave it the scientific binomial name Geoglossum cookeanum.Some authorities include an 'i' is the specific epithet, thus making Geoglossum cookeianum. apart from this alternative spelling, I know of no other synonyms of this name.

Etymology

The genus Geoglossum, set up by by Christian Hendrik Persoon in 1794, is named from Geo- meaning earth and -glossum meaning tongue - hence fungi in this genus are referred to as earthtongues (or, as some authors prefer to write it, earth tongues). The specific epithet cookeanum honours the famous British mycologist Mordecai Cubitt Cooke.

Identification guide

Geoglossum cookeanum, North Wales, UK

Fruitbody

Stromata are black, club-like, comprising a longitudinally indented fertile section above a more or less cylindrical infertile stem. The fertile section, shaped like a flattened club, covers the upper 50 to 70% of the fruitbody and is finely scurfy. Individual tongues are typically 3 to 7cm tall.

The specimen shown on the left was one of many seen in coastal dune grassland on the Isle of Anglesey, North Wales, UK during the autumn of 2011.

Asci of Geoglossum cookeanum

Asci

Cylindrical, 140-180 x 16-18µm; fairly thick walled; 8-spored.

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Spore of Geoglossum cookeanum

Spores

Ascospores elongated cylindrical to fusiform with an acute base and a rounded apex; fairly thick-walled; smooth, 55-90 x 5-7µm; multiseptate (very occasionally 6-septate but usually 7-septate).

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Spore print

Light brown.

Paraphyses of Geoglossum cookeanum

Paraphyses

Paraphyses, borne in separate clusters, are diagnostic of this species. Filiform, 2-3µm in diameter and extending slightly beyond the asci tips; not curved or coiled at the apex; base section hyaline and upper parts pale to mid brown with thicker walls and increasingly more closely septate towards tips, which comprise a chain of doliform to ovoid cells 4-6µm in diameter.

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Odour/taste

Not distinctive.

Habitat & Ecological role

On the ground in unimproved grassland and in mossy dune slacks.

Season

June to November in Britain and Ireland.

Similar species

Xylaria polymorpha is an ascomycete of similar size. It grows on dead hardwood and its stromata (compound ascomycetous fruitbodies) are not usually laterally compressed or indented.

Reference Sources

Fascinated by Fungi, Pat O'Reilly 2016.

Dictionary of the Fungi; Paul M. Kirk, Paul F. Cannon, David W. Minter and J. A. Stalpers; CABI, 2008

Taxonomic history and synonym information on these pages is drawn from many sources but in particular from the British Mycological Society's GB Checklist of Fungi and (for basidiomycetes) on Kew's Checklist of the British & Irish Basidiomycota.

Acknowledgements

This page includes pictures kindly contribited by Simon Harding.

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