Cladoxylopsids †

Earliest monilophytes

The cladoxylopsids were a geologically short-lived, fern-like group of plants, which displayed complex morphological and anatomical patterns. Compared to the contemporary plants during the late Early Devonian (Emsian), these plants were significantly larger and more complex. They formed some of the first trees on Earth during the Middle Devonian, and some ancestral members of this group may have given rise to the ferns and horsetails. Some taxa exhibited small amounts of wood surrounding individual xylem bundles. None of the members of this group exhibited planated leaves. Instead the ultimate stem tips of the plants were assumed to be photosynthetic. This group was spore-bearing; reproducing through sporangium on ultimate tips. Little is known about the gametophyte phase of this group.

Ecology & Form

Early fern-like plants
First large tree-like plants
Lived in near-shore or aquatic environments

Stems

Complex branching
Complex siphonostelic anatomy
- Plates of xylem, sometimes single and sometimes united into "U", "W" or other complex arrangements
Ultimate appendages are small and photosynthetic
Many taxa exhibit secondary xylem, but it is relatively limited compared to other vascular plants
Periderm has only been observed in Cladoxylon taeniatum
- Bark may not preserve well in these plants, or it may have been truly absent and not needed if the cortex actively grew to keep pace with growth

Roots

Strap-like roots

Leaves

No laminate leaves

Reproductive Structures

Sporangia on recurved stalks

Geologic Range

Early Devonian (Emsian) - Early Carboniferous

Classification

└Cladoxylopsida †

Gametophyte

Unknown

Diversity

The subgroups of cladoxylopsids include the following:

1. Iridopteridales †

Meyer‐Berthaud et al. (2007) exclude Iridopteridales from the Cladoxylopsida
Inclusion of Iridopteridales is a sensu lato definition of the cladoxylopsids

2. Transitional cladoxylopsids

These taxa are transitional between iridopterids and other cladoxylopsids. See below

3. Pseudosporochnales †

Mostly arbosrescent members of the cladoxylopsids

4. Cladoxylalean cladoxylosids

These taxa are considered a crown group in the cladoxylopsids

Transitional cladoxylopsids

These taxa are considered transitional between iridopterids and other cladoxylopsids

Denglongia hubeiensis †

Xue & Hao, 2008; Xue, Hao & Basinger, 2010
Late Devonian (Frasnian) of Hubei Province, China
Plant monopodial, with nodose and ridged main axis.
Dense aerial roots attached on basal nodes of main axis.
Whorls of four to six first-order branches, sterile or fertile, inserted at nodes of main axis, separated by conspicuous internodes.
- First-order branches, with proximal alternate or subopposite sterile ultimate appendages and distal whorls of second-order branches, three or four at each node.
- Sterile ultimate appendages planate or three-dimensional, composed of dichotomous branching systems, with three to six successive dichotomies.
- One or two pairs of umbrella-shaped fertile structures, attached suboppositely on proximal portions of first-order branches
- Fertile structure with an initial dichotomy forming two sister branches, along which lateral branches are alternately arranged in a pinnate pattern; each lateral branch further dichotomizing several times.
Small, fusiform sporangia in clusters of two to four, terminating short branchlets along inner side of lateral branches. Anisosporous.

Above: Reconstruction of Denglongia hubeiensis (Fig 2, Xue and Hao 2008)

Above: Anatomy of Denglongia hubeiensis † (Fig 2, Xue et al. 2010)

Below: Fertile unit of Denglongia hubeiensis † (Fig 13, Xue and Hao 2008

Foozia minuta †

Gerrienne, 1992
Lower Devonian (early Emsian) of Belgium (Bois Collet quarry, at Fooz-Wépion, northern margin of the Dinant Synclinorium)
The main axis bears numerous lateral appendages, which are 1x dichotomous
The axes several longitudinal striations; each thought to be a single vascular strand
Fertile axes terminate in one or two pairs of erect sessile sporangia.
- Sporangia are semicircular in outline and release spores identical with the sporae dispersae species Dibolisporites echinaceus
The vegetative axes display a flattened distal portions
Its flattened axes might illustrate an early stage of the evolution of the megaphyllous leaf,
- Foozia might be a possible ancestor of the Pseudosporochnales

Above: Foozia minuta † reconstruction (Fig 3, Gerrienne, 1992)

Serripteris feistii †

Rowe & Galtier, 1989
Tournaisian of France
Serripteris is probably a transitional form between the ancestral Iridopteridales and the Cladoxylopsida s.s.
Branching system consisting of "main" axis, 3.5-4.5 mm wide with laterals (second-order axes) 2 mm wide, arranged in a complex spiral. Successive laterals 20-25 mm apart, branching angle 35°
Smaller appendages (third-order axes) with circular xylem strands born proximally. The four-ribbed xylem cylinder of the main axis is 1.5 mm wide with metaxylem tracheids & protoxylem elements. Xylem strand of laterals, V-shaped, broad tangentially.

Above: Figure 5 (Rowe & Galtier, 1989) of Serripteris feistii LS26001 axis producing appendages I, I1 and III in complex spiral

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