The eastern North American species of chicken-of-the-woods has previously been featured on BPotD, Laetiporus sulphureus. Prior to the start of this decade, conventional thought was that all Laetiporus in North America were one species, Laetiporus sulphureus.
However, a closer look revealed that there were multiple species, and so Laetiporus sulphureus has been split up. In the case of today’s fungus, Laetiporus gilbertsonii is to-the-eye indistinct from Laetiporus sulphureus. Grown in culture, however, it will not reproduce with the eastern North American Laetiporus sulphureus, making it biologically distinct. By some definitions, that is enough to classify it as a separate species.
In his weblog entry, Mike mentioned that this fungus was growing on a Eucalyptus. Knowing the substrate a fungus is growing on is often useful in identifying it, and that’s the case here, as it helped eliminate the conifer-loving Laetiporus conifericola. For more on Laetiporus, visit Michael Kuo’s page on Laetiporus sulphureus and relatives. The Fungi of California site provides additional information and more photographs: Laetiporus gilbertsonii.