What are mushrooms closely related to?

Answer 1

The simple answer is that Fungi are the sister group to animals. However, the proper answer is a bit more complex than that. (It might be best to simply say fungi are closely related to animals.)

Animals and Fungi are the major clades forming the superclade Opisthokonta. One of the major synapomorphies uniting this clade is the single, posterior, whiplash flagellum on their motile cells. This feature has been lost in the late diverging branches within the fungal kingdom. It is also missing in some of the early branches that belong neither to the animal or fungal kingdoms. These branches contain protists such as the nucleariids and microsporidia, which are the true sister group to the kingdom Fungi, and choanoflagellates, which are sister to the animal kingdom. These protist groups complicate the question because they can wander and because they are early diverging. Early diverging branches are harder to classify than the so called "crown clades" (i.e. fungi, plants, animals). They form a bush at the the base of these "crown clades."

In the most recent taxonomic studies (ie. Katz et al. 2011 doi: 10.1146/annurev-micro-090110-102808 & Katz et al. 2012 doi: 10.1093/sysbio/sys026), fungi and animals do form the superclade Opisthokonta. The problematic protist groups are either left out or in between the two.

Answer 2

Mushrooms are considered to be fungi. Mushrooms are more related to animal species than they are to plant species due to cell structure.

Answer 3

The fungi is related to the mushroom.