It should be a mab. The fibrous roots are probably mycelium that is carried.

Mab (Lasiosphaera seu Calvatia) alias gray bag, horse dung bag, is a class of tambourine mycorrhizal fungi, Mabaceae fungi commonly known, widely distributed, almost everywhere in our country, summer and autumn seasons after the rain, most often grow in the wilderness meadow or wetland on rotting wood.

Mab like sandy loam and decaying trees, fallen leaves, dung grass and other organic matter, like high temperature and high humidity environment, the base of its seed entities have rhizomatous mycelial cord fixed on sandy soil. Generally in late summer, after the fall rains, in the rainy months of July and August, born in the bushes, as well as the underground layer of dead branches and leaves, rotting grass, wetland rotting wood on the rotting mucilage and other organic matter, only suitable for the survival of the environment is better in mountainous areas or semi-mountainous areas.

Extended information

A mushroom picker in Bashkortostan*** and State of the Russian Federation found a giant Mab mushroom.

Svetlana, a researcher at the Center for Botanical Research of the Russian Academy of Sciences, said she had never seen such a huge mushroom in the region, but had heard of a 30-kilogram mushroom found elsewhere. The mushroom is considered a "devil's mushroom" because no one knows how it appeared or when it will disappear, she said.

It is believed that these mushrooms are usually found between August and October in open areas such as forests, fields and grasslands.

Svetlana also said that these mushrooms are edible when they are initially resilient. If they turn yellow or brown, or even rot. It would be best not to pick them.

Baidu Wikipedia - Mabo

People's Daily Online - Giant 'Devil's Mushroom' Mabo Mushroom Weighs 10 Kilograms