Public Description of Annulohypoxylon thouarsianum (Lév.) Y.M. Ju, J.D. Rogers & H.M. Hsieh

Title: Public Description (Default)
Name: Annulohypoxylon thouarsianum (Lév.) Y.M. Ju, J.D. Rogers & H.M. Hsieh
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Description status: Unreviewed

Taxonomic Classification:

Domain: Eukarya
Kingdom: Fungi
Phylum: Ascomycota
Class: Sordariomycetes
Order: Xylariales
Family: Hypoxylaceae

General Description:

This is probably the most commonly encountered large, hemispherical Annulohypoxylon in North America. It has large (from about 0.5 cm up to about 5 cm diameter; typically 1-2 cm) hemispherical to spherical stromata with mostly inconspicuous perithecial mounds, and is black or dark brown in colour with very dark granules immediately beneath the hard outer crust (visible with dissecting microscope). The interior tissues have a vaguely zoned appearance, with radial structure from the attachment point, and are woody or hard-corky in texture; the interior has much the same feeling as well a piece of charcoal. There are dull green pigments extractable with 10% KOH.

The perithecia are obvoid or sub-globose, 0.3-0.7 mm diam x 0.5-1.3 mm high. The ostioles are slightly papillate, with an obvious annular (truncatum-type) disc, about 0.2-0.5 mm in diameter.

The ascospores are brown, unicellular, ellipsoid-inequilateral (like a flattened football), with narrowly rounded ends. The measure 14-24 × 4-5.5 µm, with straight, spore-length germ slit on the flattened (less curved) side of the spore. The also have a perispore (clear layer around the spore) that does not dehisce in 10% KOH; both the perispore and the epispore are smooth (no noticeable texture).

Diagnostic Description:

Pretty much anyone in the USA that finds one of these big hemisphaerical Annulohypoxylon assumes it’s A. thouarsianum, but there are two other species with similar gross morphology: A. annulatum and
A. hians.

You pretty much have to look at the spores to tell them apart; here’s how you do it: A. thouarsianum has much longer ascospores than either of the other two (14-24 µm vs. 7.5-10.5); the other two also have their germ slit on the curved side instead of the flat side of the spore. Additionally, A. hians has either purple or no apparent KOH extractable pigments, while A. thouarsianum and A. annulatum should have very obvious green (dull, brownish, olivaceous) KOH extractable pigments.

There is also a variety, A. thouarsianum var. macrosporum, that has even longer ascospores (24-30 µm) than the typical variety. This is only known from Mexico.

It is easy to confuse these large hemispherical Annulohypoxylon with Daldinia, another genus of Xylariaceae. The vague zonation of the woody interior flesh is confusing when keying out Xylariaceae: distinct zonation of the interior flesh is an identifying feature of the genus Daldinia! The “zonation” present in this and similar species is not true zonation, as in the Daldinia, where a cross-section will reveal very distinct alternations of black and white zones, or similar. If in doubt, look for the annular discs, which are always present in Annulohypoxylon, and always absent in Daldinia.


American and African distribution. Has been collected from Mexico, both the East and West coasts of the USA, South Africa, Tanzania, and Ecuador (the Galapagos).


Found on dead angiosperm wood, usually corticate, usually fairly large diameter. Seems to be particularly common on Fagaceae wood; associated with trees killed by Sudden Oak Death in California.

Look Alikes:

C. G. Lloyd, Mycol. Writings 5: 26. 1919
Ju, Y. M., & Rogers, J. D. (1996). A revision of the genus Hypoxylon (pp. 365-365). St Paul, Minnesota,, USA: APS Press.
Hsieh, H. M., Ju, Y. M., & Rogers, J. D. (2005). Molecular phylogeny of Hypoxylon and closely related genera. Mycologia, 97(4), 844-865.
Miller, J. H. (1961). A monograph of the world species of Hypoxylon.

Description author: Roo Vandegrift (Request Authorship Credit)
Description editor: Erlon

Created: 2010-02-26 15:01:53 CST (-0500) by Erlon (Herbert Baker)
Last modified: 2015-02-11 18:00:07 CST (-0500) by Roo Vandegrift (Werdnus)
Viewed: 266 times, last viewed: 2019-03-16 03:44:35 CDT (-0400)