Metzgeriales - Classification

Classification

The beginning of modern liverwort nomenclature is marked with the 1753 publication of Linnaeus' Species Plantarum, although this relied heavily upon the prior work of Micheli (1729) and Dillenius (1741). Linnaeus included all 25 known species of liverworts, together with mosses, algae, and fungi, within a single class Cryptogamia. 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. 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. The same five subgroups of "Frondosae", without significant change, were used in the Synopsis Hepaticarum of Gottsche, Lindenberg, and Nees.

A more thorough understanding of the Metzgeriales was not achieved until the morphological and developmental work of Leitgeb in the late nineteenth century. Leitgeb was among the first to recognize and appreciate the significance of development and reproductive morphology as a guide to distinguishing liverwort groups. His careful examinations guided revisions made in the classification published from 1893 to 1895 by Schiffner in Engler and Prantl. Schiffner thus divided his "Jungermanniales" into two broad groups according to whether the archegonia were terminal on reproductive branches (Jungermanniales akrogynae) or sub-terminal (Jungermanniales anakrogynae). This latter group included what are now recognized as the Metzgeriales, Sphaerocarpales, and Haplomitriales.

The simple thalloids were not given ordinal status until 1930 by Chalaud. Although subsequent systems similarly treated the group as distinct, the name of the order was more often given as "Jungermanniales anacrogynae" (or similar), or the group was retained within the Jungermanniales as a suborder with either this name or the name "Metzgerineae". The highly influential and comprehensive 1966 classification found in Schuster's Hepaticae and Anthocerotae of North America firmly established the name "Metzgeriales" for the group, although he had used this name in his earlier works. Schuster revised his system in 1972 and again in 1984. The only change he made in the circumscription of the Metzgeriales was to remove the Treubiales in accordance with that change made in the classification of Schljakov.

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. The classification of Crandall-Stotler and Stotler (2000) adopted several of Schljakov's orders, while revising their membership and grouping them within a subclass "Metzgeriidae". These changes reflected a morphological analysis of species that had been presented three years earlier. 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 remnant of the group, after the removal of these taxa, consists of their Metzgeriales (7 families), Fossombroniales (4 families), and the Phyllothalliaceae.