First Mystery Solved! It's Hypoxylon thouarsianum! (it's also a mouthful!)

For those who recall, on 23 November 2008, I posted two sets of Mystery Phenomena on this blog, and asked if anyone could identify them for me. Well, luckily for me today, while spending some time at the Nix Nature Center, I came across photos of both Mystery Phenomena in the USDA's Publication, A Field Guide to Insects and Diseases of California Oaks (July 2006). Here's one of the two mysteries, solved! Click on the link to see the photos, and read all about it below!


Hypoxylon thouarsianum (Click Here to Access NIOC's photos)

Hypoxylon thouarsianum

Distribution/ Hosts

Hypoxylon thouarsianum occurs throughout much of California. Its reported range also includes the southeastern US, Central and South America, and parts of Africa, including South Africa and Tanzania. It occurs on CA black, blue, coast live, interior live, canyon live, and valley oak, as well as tanoak. It is occasionally found on other species including hackberry and avocado.

Symptoms

Black hemispherical fruiting bodies (stromata) of Hypoxylon thouarsianum develop, sometimes in great numbers, on the surface of dead bark or wood. The fungus causes a white rot of the sapwood of living trees and dead wood. Sapwood decay caused by Hypoxylon thouarsianum in trees affected by Phytophthora ramorum canker may be quite extensive and may lead to branch or trunk failure.

Agent Description

Immature stromata that emerge through the bark over wood colonized by Hypoxylon thouarsianum are initially rounded, black, smooth, and glossy and covered with a thin, fragile membrane. This short-lived membrane ruptures, revealing a layer of powdery, dark olive green asexual spores (conidia) on the surface of the new stroata.

Importance

This fungus appears to be of little consequence in healthy trees, but can quickly overrun severely stressed tres and trees with extensive Phytophthora ramorum cankers. Sapwood decay caused by this pathogen probably plays a role in rapid tree death that occurs in some Phytophthora ramorum-infected trees.
(Information taken from pages 102-105)