They aren't plants but they sure do act like plants. Fungi are different from plants in several ways. Fungi need already formed foodstuffs. In other words they like to eat what others have made. However, this is good because when plants and animals die someone has to get rid of the remains.
Fungi have long thin cells that are very similar thoughout the entire body of the fungus.
Plants have many different types of cells that make up different plant parts like leaves, roots, stems, etc. Lastly, fungi have a chitin containing cell wall rather than a cellulose containing cell wall as is seen in plants. That is because these organisms are the first ones I have talked about that have organelles . Remember, viruses and bacteria are gutless. The fungi are one of the eukaryotic organisms microbiologists study.