Cladoniaceae

The Cladoniaceae are a family of lichen in the order Lecanorales. It is one of the largest families of lichen-forming fungi, with about 560 species distributed amongst 17 genera. The reindeer moss and cup lichens (''Cladonia'') belong to this family. The latter genus, which comprises about 500 species, forms a major part of the diet of large mammals in taiga and tundra ecosystems. Many Cladoniaceae lichens grow on soil, but other can use decaying wood, tree trunks, and, in a few instances, rocks as their substrate. They grow in places with high humidity, and cannot tolerate aridity.

Many Cladoniaceae species are characterized by a thallus that has two distinct forms: a scaly or crust-like primary thallus that, depending on the species, can be permanent or temporary, and a secondary fruticose thallus called a podetium or pseudopodetium. Cladoniaceae members form symbiotic associations with green algae from the class Trebouxiophyceae, usually the genus '' Asterochloris''. Five Cladoniaceae species are included in the International Union for Conservation of Nature's Red List of Threatened Species.

Taxonomy

Cladoniaceae was formally introduced to science in 1827 by German naturalist Jonathan Carl Zenker in a publication of Karl Goebel. Zenker's initial concept of the family included genera that are now recognized as separate families, including Baeomycetaceae, Icmadophilaceae, and Stereocaulaceae. William Nylander included 53 ''Cladonia'' species worldwide in his 1860 work ''Synopsis lichenum''. When Edvard August Vainio published his three-volume monograph on the Cladoniaceae (''Monographia Cladoniarum universalis'', 1887, 1894, and 1897), he included 134 species and subspecies. In his circumscription of the family, the genera ''Pycnothelia'', ''Cladia'', and ''Cladina'' were included in the genus ''Cladonia''.

Cladoniaceae is now one of the largest families of lichen-forming fungi, with about 560 species distributed amongst 18 genera. The type genus, after which the family was named, is ''Cladonia'', circumscribed by Irish physician and botanist Patrick Browne in 1756. He included 8 species in his new genus. Of their occurrence, he wrote: "All these species are found in great abundance in the mountains of Liguanea: they grow mostly on the ground, among other sorts of moss, but a few ... species chiefly are found upon the decaying trunks of trees."

Synonymy

Several phylogenetic studies have shown that Cladoniaceae is a member of the order Lecanorales, and is closely related to the family Stereocaulaceae. The family Cetradoniaceae, which was created in 2002 to contain the endangered species '' Cetradonia linearis'', was folded into the Cladoniaceae in 2006.

In 2018, Kraichak and colleagues used a technique called temporal banding to reorganize the Lecanoromycetes, proposing a revised system of classification based on correlating taxonomic rank with geological (evolutionary) age. They synonymized the families Squamarinaceae and Stereocaulaceae with the Cladoniaceae, resulting in a large increase in the number of genera and species. The Squamarinaceae had already been included in the Cladoniaceae by previous authors. Although this reorganization has been used in some later publications, the folding of the Stereocaulaceae into the Cladoniaceae was not accepted in a recent analysis. As Robert Lücking explained, "merging of the two families under the name Cladoniaceae is not possible without a conservation proposal because Cladoniaceae (Zenker, 1827) is antedated by Stereocaulaceae (Chevallier, 1826) by one year."

Description

The thallus of Cladoniaceae lichens are fruticose or foliose, and are often dimorphic–consisting of two distinct forms. The primary thallus is ephemeral to persistent, crustose, foliose or squamulose, while the secondary thallus is typically vertical and holds the ascomata. The secondary thallus ranges in height from a few millimetres to more than . Some species, however, form neither a primary thallus nor any fruticose structures.

The ascomata are in the form of an apothecium, and are biatorine, meaning they are of the lecideine