Collema tenax is a species of lichen known by the common names jelly lichen, black lichen, and desert lichen. It occurs in Arctic and temperate regions in the Northern Hemisphere.^[1] It is very common in North America, and it is present in Europe, Asia, and Africa. It is the most widely distributed Collema.^[2]

This lichen has a thick black or dark green gelatinous thallus which is variable in size. It is generally 1 to 3 centimeters wide.^[2] It contains a symbiont, the cyanobacterium Nostoc commune. It reproduces when pieces of the thallus break off, or when isidia, soredia, and apothecia are produced.^[1] It is tolerant of desiccation, shrinking when dry and swelling up when water is present.^[2]

This lichen is terricolous, growing on the soil surface. It is an indicator of basic soils, and is often found on gypsum-rich and other calcareous soils. It is a common component of cryptobiotic soil crusts, for example, in the dry regions of the western United States. It fixes nitrogen, increasing the nitrogen levels in the soil.^[1]