Answer: This is the earth star fungus. See these web pages for more information: http://herbarium.usu.edu/fungi/FunFacts/starfact.htm and http://www.shelterpub.com/_shelter/lost.html (scroll down to the "earth star barometer" section)

This group of fungi is saprophytic, i.e. it grows on dead organic matter in the soil. Most of the organism is below soil level as mycelium (threads of the fungus). The part in your photograph is the reproductive structure. It is somewhat related to mushrooms. I do not know much about poisonous mushrooms, but I would assume all are poisonous unless you have an expert in this field identify it. It will not harm you when working in the garden. Ignore it and it will soon decompose and disappear.
Mark Black, Plant Pathologist