They once were... Most taxonomists today place them in the Kingdom Fungi, but because many species have structures that are roughly analagous to plant parts it easy to understand why people would think of them as plants.

Mike

Actually, modern science would consider fungi to more akin to animals than plants, believe it or not. Strange but true! But since they are clearly not animal (brain and nervous system and all that kind of stuff), and clearly not a plant....they belong in their own kingdom.

Other characteristics that separate them from plants is that they are heterotrophic and cannot make their own food as most plants do. Fungi don't have stomachs so must pre-digest their organic compounds outside the 'body' before absorbing it. They also don't have chlorophyll, as do most plants. They often (not always) have rigid cell walls like those of plants BUT a component of those walls is chitin....common to insects and other arthropods! How did THAT happen, I'd like to know? ;-)

The same way the platypus happened... a bit of this and a bit of that... only instead of across species, this was across kingdom! LOL

Science has come a long way since I was in school. This question and the comments made me do a little research on classifications and I was amazed at just how much has changed. I only remember plant and animal kingdoms. Now there are 3 domains and 4 kingdoms! I wonder what the next 50 years of research will bring? Sure would like to be here to see it.

Here is a link that might be useful: Classification of living things

This stuff fascinates me. The ultimate evidence that fungi are a group all their own, distinct from and equal in status to plants and animals, is genetic. Examining DNA from equivalent and very slowly changing regions of plant, animal and fungus genomes builds a clear picture of fungi as the closest relatives of the animals, the two kingdoms having split as members of the 'eukaryotic crown group' around one billion years ago! Of course the gardening literature still often refers to them as 'lower plants', which is a mistake.

I for one am all for including ornamental & edible fungi in the gardening landscape; they've been neglected for too long.

Here is a link that might be useful: Tree of Life