The Sawdoniales are an

order Order, ORDER or Orders may refer to: * A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica * Categorization, the process in which ideas and objects are recognized, differentiated, and understood ...

plesion In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. ...

of extinct

zosterophyll The zosterophylls are a group of extinct land plants that first appeared in the Silurian period. The taxon was first established by Banks in 1968 as the subdivision Zosterophyllophytina; they have since also been treated as the division Zostero ...

s. The zosterophylls were among the first

vascular plant Vascular plants (), also called tracheophytes (, ) or collectively tracheophyta (; ), are plants that have lignin, lignified tissues (the xylem) for conducting water and minerals throughout the plant. They also have a specialized non-lignified Ti ...

s in the fossil record, and share an ancestor with the living lycophytes. The group has been divided up in various ways. In their major

cladistic Cladistics ( ; from Ancient Greek 'branch') is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is ...

study of early

land plants The embryophytes () are a clade of plants, also known as Embryophyta (Plantae ''sensu strictissimo'') () or land plants. They are the most familiar group of photoautotrophs that make up the vegetation on Earth's dry lands and wetlands. Embryophy ...

, Kenrick and Crane placed most of the zosterophylls in the Sawdoniales (which they treated as a

). Like other zosterophylls, members of the Sawdoniales bore lateral, reniform sporangia. They branched dichotomously, and grew at the ends by unrolling ( circinate vernation). Some had smooth stems, others were covered in small spines; fungal bodies have been reported in some spines.

Taxonomy

In 1997, Kenrick and Crane placed most of the zosterophylls in the plesion Sawdoniales, characterizing the group as having "marked bilateral symmetry". Their summary cladogram did not resolve the taxa within the Sawdoniales, other than placing '' Zosterophyllum divaricatum'' within the zosterophylls but outside the Sawdoniales. Hao and Xue in 2013 criticized their approach, and placed many of the members of Kenrick and Crane's Sawdoniales in the order

Gosslingiales Gosslingiales is an Order (biology), order of extinct zosterophylls. The zosterophylls were among the first vascular plants in the fossil record, and share an ancestor with the Lycopodiopsida, living lycophytes. The group has been divided up in ...

, characterized among other features by the absence of terminal sporangia (i.e. with only lateral sporangia), and hence indeterminate growth.

Families

In Kenrick and Crane's treatment, the Sawdoniales are divided into four families: * †

Gosslingiaceae Gosslingiaceae is a family of extinct zosterophylls. The zosterophylls were among the first vascular plants in the fossil record, and are considered to share an ancestor with the living lycophytes. The family is variously placed in the order Sa ...

* †

Sawdoniaceae Sawdoniaceae is a family of extinct zosterophylls. The zosterophylls were among the first vascular plants in the fossil record, and are considered to share an ancestor with the living lycophytes. The family is recognized by some sources, and pl ...

* † Barinophytaceae * † Hsuaceae Hao and Xue place the first two families in their Gosslingiales, but exclude both the Barinophytaceae and the Hsuaceae from the zosterophylls.

References

Bibliography

* *

External links

* Silurian plants Devonian plants Prehistoric lycophytes Prehistoric plant orders Paleozoic life of New Brunswick Zosterophylls Lycophyte orders {{Devonian-plant-stub