Although these plants are almost entirely restricted to regions with high humidity or readily available moisture, the group as a whole is widely distributed, and occurs on every continent except Antarctica.

Because these plants are thin and relatively undifferentiated, with little evidence of distinct tissues, the Metzgeriales are sometimes called the "simple thalloid liverworts".

The genus Phyllothallia has a more striking leafiness, with paired lobes of tissue spaced regularly at swollen nodes along a central, forked stem.

Although these plants are almost entirely restricted to regions with high humidity or readily available moisture, the group as a whole is widely distributed, and occurs on every continent except Antarctica.

[10] The beginning of modern liverwort nomenclature is marked with the 1753 publication of Linnaeus' Species Plantarum,[11] although this relied heavily upon the prior work of Micheli (1729)[12] and Dillenius (1741).

Linnaeus' system was heavily revised by workers in the early nineteenth century, so that by the time Endlicher published his Enchiridion Botanicum in 1841, five orders of liverworts were defined, and the "Frondosae" were segregated as a group that is congruent with the modern concept of the Metzgeriales.

[14] Endlicher's "Frondosae" included five subgroups (Metzgerieae, Aneureae, Haplolaeneae, Diplomitrieae, and Codonieae) with no assigned taxonomic rank, but these groups were termed Familien by Dědeček in 1886.

[24] Schljakov's 1972 classification had elevated several subordinal groups within the simple thalloids to the rank of order, and treated the Metzgeriales itself as a superorder "Metzgerianae", but Schuster's 1984 system rejected most of these changes.

[25] Although their system changed the rank and the Latin ending of the name, the composition was identical to the Metzgeriales of Schuster (1966), with only the addition of the Haplomitriales to its membership.

Subsequent studies incorporating DNA sequence analysis have removed the Haplomitriales, Treubiales, and Blasiales and place those taxa elsewhere.

The Blasiaceae has been assigned its own order Blasiales, and phylogenetic studies show that it is more closely related to the Marchantiales than to members of the Metzgeriales.

[21] This work included a considerable description sufficient to distinguish the order from all others, but Schuster relied on the 1972 emendation by Schljakov[24] to provide the Latin diagnosis required by the International Code of Botanical Nomenclature.

[6] In the publication of their revised liverwort classification in 2000, Crandall-Stotler and Stotler agreed with Schuster as to the attribution of the name, although they restricted their circumscription of the order considerably.

[26][27] Specifically, the Jungermanniales (leafy liverworts) are more closely related to the Aneuraceae and Metzgeriaceae than are other simple thalloid groups.

[30] The genus Sandeothallus and the species Mizutania riccardioides and Vandiemenia ratkowskiana (each the only member of its respective family) were not included in the study.

Haplomitriales Treubiales Blasiales Sphaerocarpales Marchantiales Jungermanniales Pleuroziaceae Aneuraceae Metzgeriaceae Pelliaceae Calyculariaceae Makinoaceae Allisoniaceae Fossombroniaceae Petalophyllaceae Phyllothalliaceae Hymenophytaceae Moerckiaceae Pallaviciniaceae Sandeothallaceae Because plants belonging to the Metgeriales lack hard tissues, and the plants often decay or die back, preservation of fossils is dependent upon rapid burial by floods or volcanic ash.

[37] Bryophytes are considered "delicate" plants, and this characteristic is often cited as the reason for the apparently poor fossil record of the group.