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Earliest monilophytes
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
Ecology & Form
Early fern-like plants
First large tree-like plants
Lived in near-shore or aquatic environments
Stems
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
Roots
Strap-like roots
Leaves
Leaves
No laminate leaves
Reproductive Structures
Reproductive Structures
Sporangia on recurved stalks
Geologic Range
Geologic Range
Classification
Classification
└Cladoxylopsida †
Gametophyte
Gametophyte
Unknown
Diversity
Diversity
The subgroups of cladoxylopsids sensu lato include the following:
Meyer‐Berthaud et al. (2007) exclude Iridopteridales from the Cladoxylopsida
Inclusion of Iridopteridales is a sensu lato definition of the cladoxylopsids
2. Early & transitional cladoxylopsids
2. Early & transitional cladoxylopsids
These taxa are transitional between iridopterids and other cladoxylopsids.
See below (e.g., Adelocladoxis, Denglongia, Foozia, Serripteris)
Mostly arboreous members of the cladoxylopsids
These taxa are considered a crown group in the cladoxylopsids
Above: Phylogeny of the cladoxylopsids s.l. (including the iridopterids) during the Devonian and early Carboniferous (Dureiux, et al., 2021, Fig. 9)
Above, left & center: Phylogeny of the cladoxylopsids s.l. (including the iridopterids) showing the evolution of morphological and anatomical features (Dureiux, et al., 2021, Fig. 10-11)
Above, right: Simplified phylogenetic tree of the cladoxylopsids from Chu et al. (2024, fig. 51) with discussed stele and ultimate appendages characters mapped
Transitional cladoxylopsids
Transitional cladoxylopsids
These taxa are considered transitional between basal iridopterids and other derived cladoxylopsids
Adelocladoxis praecox †
Adelocladoxis praecox †
Mid- to late Emsian of the Battery Point Formation, Quebec, Canada
This taxon is some of the earliest anatomical evidence of cladoxylopsids
Axes, 1–1.5mm thick
Primary xylem is an actinostele with five or six lobes that protrude from the central area
Phloem layer thin around xylem, with thin-walled fusiform cells
Epidermal cells with robust primary walls and secondary metabolite content fossilized inside as solid rods of dark, compact material
Xylem traces to ultimate appendages hourglass-shaped, tangentially elongated
Ultimate appendages isotomously branched at least twice, some with recurved tips.
Sporangia erect, attached at tips of ultimate appendage segments, fusiform,
Above: Adelocladoxis praecox † main axis anatomy (Durieux et al., 2021, Figure 1)
Denglongia hubeiensis †
Denglongia hubeiensis †
Xue & Hao, 2008; Xue, Hao & Basinger, 2010
Late Devonian (Frasnian) of Hubei Province, China
Denglongia was probably a transitional or stem cladoxylopsid closely related to iridopteridaleans
If iridopterids arose earlier than the psedusporochnalean cladoxylopsids, then Denglongia might represent a "holdover" taxon from the evolution of an iridopterid-grade form to a cladoxylopsid-like form
Plant monopodial, with nodose and ridged main axis.
Dense aerial roots attached to basal nodes of the 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 the 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 †
Foozia minuta †
This taxon is the earliest evidence of cladoxylopsids
Foozia might be a possible ancestor of the Pseudosporochnales
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 bear 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 flattened distal portions
Its flattened axes might illustrate an early stage of the evolution of the megaphyllous leaf
Above: Foozia minuta † reconstruction (Fig 3, Gerrienne, 1992)
Rhipidophyton acanthum †
Rhipidophyton acanthum †
Berry and Wang, 2006
Plants with substantial upright stem; sterile branches ramified with close dichotomies (digitate) proximally, with more distantly separated distal dichotomies and recurved tips, lacking appendages;
Fertile axes unbranched, with spirally inserted fertile appendages; fertile appendages consisting of a central axis with a proximal pair of adaxial sporangia, distally flattened and dissected with sporangia arranged in a fan shape on either side of the dissection, two pairs on each side; sporangia elongate-elliptical with a slightly pointed apex, dorsoventrally flatted
Above: Rhipidophyton acanthum † reconstruction (Fig 3, Gerrienne, 1992)
Serripteris feistii †
Serripteris feistii †
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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