Often casually called "the Meadow Mushrooms," about 90% of Agaricus species actually reside in forest and other non-grassland habitats. All species exploit the partly decomposed remains of green plants. Some species are edible, even cultivated, while others are toxic. 

Richard W. Kerrigan became interested in Agaricus in 1971, while an undergraduate, when he couldn't find any published descriptions of a poisonous Agaricus that he was finding regularly. He ultimately identified it to be Agaricus californicus, a species that had vanished from the literature for the better part of the 20th century. 

Richard has continued to work on the diversity, taxonomy, and phylogeny of Agaricus for the last 45 years, both in academic settings and as Director of Research with Sylvan, Inc., the world's leading producer of cultivated mushroom spawn. In 2016, he published the book Agaricus of North America.