Genetic studies confirm that fungi diverged from plants and animals about 1 billion years ago. They are in fact more closely related to animals than they are to plants. Unlike plants that have cell walls containing cellulose, fungal cell walls contain chitin, like many insects and lobsters and crabs. They have had a symbiotic relationship with plants in the earliest stages of terrestrial evolution when vascular plants were no more than a couple of feet tall. In fact, they began to colonize the land over 400 million years ago, before the first vertebrates came out of the sea and before plants colonized the soil. In fact, the first plants had no roots. At least one mushroom, Prototaxites, was a giant at 26 feet tall. It is believed to have been a Basidiomycete that looks similar to a modern day Clavariadelphus.