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 Coenopteridophyta) in his cladistic analysis and all of the extinct forms emerge as separate groups from the extant ferns.  Indeed, these organisms emerge as sisters to the Sphenophyta, Progymnospermophyta, and part of the Cornopteridophyta (the Zygopteridales).

The cladoxylids were monopodial with small microphylls and spore-bearing frond-like branching systems.  Thus, they resembled the Trimerophytophyta.  All extinct, these organisms flourished during the Devonian but died out by its end.  Pearson (1995) believed that the cladoxylids gave rise to the Progymnospermophyta and the seed plants.  I have modified the taxonomic systems of Bold et al. (1987) and Bierhorst (1971) in the organization of this phylum.

I. PHYLUM CHARACTERISTICS

A. Structure

Gametophyte: Not known.

Sporophyte: Tree-like with monopodial branching.

Spores: Not known.

Sporangia: Thick-walled eusporangia which dehisce longitudinally. Sporangia occur on fertile appendages.

Stele: Complex; stems tend to be polystelic.

Leaves: Leaves are restricted to small enations or microphylls which occur on large branching systems which resemble fronds.

Roots: Not known.

B. Ecology: Plants are extinct.

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

ORDER CLADOXYLALES

These plants are extinct. They have 2 types of leaf-like appendages (microphylls). The sterile appendages are small andhave open branching. The blade-like fertile appendages are flattened and dichotomously branched, each fertile branch terminates in a small sporangium.

example: Cladoxylon

ORDER PSEUDOSPOROCHNALES

These plants are extinct with a fossil history which ranges through the Devonian. These plants are very large with a growth habit which resembles a tree fern. The branches resemble large fronds with sterile and fertile dichomously branched appendages. The fertile appendages are not flattened.

example: Pseudosporochnus

ORDER CALAMOPHYTALES

These plants are extinct and known from the middle Devonian. The plants show strong monopodial growth with dichotomizing ultimate branches. The microphylls are round in cross section and spirally arranged on the stems. Sporangia occur on clusters of recurved stems (these structures resemble sporangiophores).

example: Calamophyton

revised: 04/15/2003