The majority of species in Armillaria, a genus of fungi commonly known as honey mushrooms, are saprotrophic and live mainly on dead wood, but some are parasites that can cause root and butt rot in over 600 species of woody plants. Some Armillaria species, such as A. gallica (pictured), A. mellea, and A. tabescens, are bioluminescent. The genus once served as a wastebasket taxon; due largely to differing interpretations on the limits of the genus, over 270 species and varieties have been placed in Armillaria. A comprehensive 1995 study by Tom Volk and Harold Burdsall evaluated all of the epithets that have been used in Armillaria. They determined that about 40 species belong to Armillaria sensu stricto; the remaining names belong to species that are distributed among 43 other modern fungal genera. Many species are difficult or impossible to distinguish from each other using observable characteristics. (Full list...)