These are from the groups of plants called preferns.  Bold et al (1987) and most authors treat them as if they were a subgroup of ferns.  However, Rothwell (1999) includes both groups of preferns (the other one is the Cladoxylidophyta) in his cladistic analysis and all of the extinct forms emerge as separate groups from the extant ferns.  Indeed, these organisms emerge as paraphyletic in his analysis.  The Stauropteridales emerge near the base of the cladogram while the Zygopteridales occur in the same clade as the cladoxylids.

The coenopterids were monopodial with spore-bearing frond-like branching systems that may have been the earliest macrophylls.  Thus, they resembled tree ferns.  These plants flourished from the Devonian to the end of the Permian when they died out.  Pearson (1995) treated the Coenopteridophyta as the group from which the leptosporangiate ferns arose.  I have modified the taxonomic systems of Bold et al. (1987) and Bierhorst (1971) in the organization of this phylum.  However, if Rothwell (1999) is correct, this system will require considerable revision.

I. PHYLUM CHARACTERISTICS

A. Structure

Gametophyte: Not known.

Sporophyte: Tree-like with monopodial branching.

Spores: Homosporous to heterosporous.

Sporangia: Thick-walled eusporangia which dehisce at the apex of the sporangium. Some sporangia in synangia.

Stele: Protostelic to siphonostelic; usually complex.

Leaves: Difficult to interpret; the ultimate branches appear to be frond-like and some interpret them as the earliest macrophylls.

Roots: Present, probably adventitious.

A. Ecology: Plants are extinct.

II. TAXONOMY: As I have defined them, the coenopterid preferns have one class: COENOPTERIDOPSIDA and three orders.

ORDER STAUROPTERIDALES

These plants are extinct with a fossil history through the Carboniferous. They grow as a trichotomizing axis which forms a bushy plant. Elongate sporangia occur on some of the ultimate branches. The sporangia dehisce by an opening at the apex of the sporangium.

example: Stauropteris

ORDER RHACOPHYTONALES

These plants are extinct with a fossil history which ranges through the Carboniferous. These plants are have a slender stem and large frond-like appendages. They were probably creeping. The sterile fronds have primary pinnae in 2 ranks, each of which has small, dichotomously branching stems around the pinnna. The fertile fronds are more complex; some primary pinnae are sterile, the fertile primary pinnae bear ball-like dichotomously branched appendages, each of which terminates in elongate sporangia.

example: Rhacophyton

ORDER ZYGOPTERIDALES

These plants are extinct and known from the upper Devonian to the Permian. The plants are creeping or rhizomatous. The rhizomes are covered with frond-like dichotomizing branches which occur in two ranks. The stele is H-shaped in mature stems and shows evidence of secondary growth. The sporangia are at the tips or on the abaxial surface of the ultimate branches.

example: Zygopteris

revised: 04/15/2003