Arbarum

Arbarum is a genus of fungi belonging to the family Sclerodermataceae. These fungi are characterized by their robust, leathery fruiting bodies, which are often roughly spherical or irregularly shaped. The outer layer of the fruiting body, known as the peridium, is typically thick and firm, sometimes becoming brittle with age. Internally, the gleba, which contains the spores, is often powdery or becomes so as it matures. The spores of arbarum species are generally dark in color, often brown or black, and are typically echinulate or verrucose, meaning they have small spines or warts on their surface.

Species within the genus arbarum are often found growing in terrestrial environments, typically in association with trees, forming mycorrhizal relationships. They are widespread in various climatic regions, though specific distribution patterns can vary between species. The common name "earthballs" is sometimes used for members of this genus and related genera due to their appearance and growth habit. Identification of arbarum species often relies on macroscopic features of the fruiting body, such as size, shape, peridium texture, and internal gleba characteristics, as well as microscopic examination of spore morphology. Their ecological role primarily involves nutrient cycling in forest ecosystems.