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Plants with fern-like anatomy, but lacking leaves
Plants with fern-like anatomy, but lacking leaves
Iridopteridales was erected by Stein (1982) based on anatomical characters of permineralized axes. They were early fern-like/horsetail-like plants, which had complex anatomy, but no laminate leaves. The branches came off in a whorled pattern with recurved stem tips. The combination of morphological and anatomical features suggests that this group may have given rise to the ferns and horsetails. The plants of this group are potentially intermediate between Early Devonian basal euphyllophytes (Kenrick and Crane, 1997) and the more complex Late Devonian/Mississippian major groups, for example, sphenopsids and ferns (Arnold, 1940; Skog and Banks, 1973; Stein et al., 1984; Berry & Stein, 2000).
Ecology & Form
Ecology & Form
Most iridopterids are Middle Devonian and come from Laurentia (North America, Svalbard)
Stems
Stems
Anatomy has a highly dissected, ribbed actinostele with permanent protoxylem strands and whorled trace departure (Berry and Stein 2000; Taylor and Taylor 2008)
Xylem is mesarch
Metaxylem tracheids are large in the central part of the primary xylem ribs; smaller at the periphery
Vascular supplies to both the appendages and the lateral branches are provided by a single xylem rib and originate as a single trace
Proximal axes are pseudomonopodial
Lateral axes are iterative and whorled
Distal axes are isotomous and recurved
Leaves
Leaves
Leafless
Roots
Roots
Unknown
Reproduction
Reproduction
Sporangia in pairs on recurved axes
Classification
Classification
Embryophytes
└Iridopteridales †
Meyer‐Berthaud et al. (2007) excluded Iridopteridales from the Cladoxylopsida
Geologic Age
Geologic Age
Middle Devonian - early Late Devonian (Frasnian)
Above: Vascular system of Iridopteridales and allies in transverse section. (A)(B) Iridopteris eriensis. (C)(D) Arachnoxylon minor. (E)(G) Metacladophyton tetraxylum. (H) Compsocradus laevigatus. (I) Asteropteris noveboracensis. (J)(L) Arachnoxylon kopfii. (M) Ibyka amphikoma. (N) Metacladophyton ziguinum. (O) Keraphyton mawsoniae. (P) Denglongia hubeiensis. (Q) Rotoxylon dawsonii. (R) Serripteris feistii. (S) Dixopodoxylon goense. Scale bar five mm. Secondary-type xylem in dark grey. (A)(D), (I) (M): adapted from Stein (1982); (E)(G): adapted from Wang & Geng (1997); (H): adapted from Berry & Stein (2000); (N): adapted from Wang & Lin (2007); (P): adapted from Xue, Hao & Basinger (2010); (Q): adapted from Cordi & Stein (2005); (R): adapted from Rowe & Galtier (1989); (S) adapted from Fairon-Demaret (1969).
Diversity
Diversity
Anapaulia moodyi †
Anapaulia moodyi †
Berry & Edwards, 1996
Devonian of Venezuela
Monopodial main axis has both large second-order axes and smaller dichotomizing branches inserted in a predominantly whorled arrangement. Long internodes separate the whorls.
Third-order axes and small fourth-order axes are born in compressed helices
Small ultimate branching system that dichotomizes up to four times are borne on the third- and fourth-order axes in helices and compressed helices.
Elliptical sporangia are borne upon the recurved tips of ultimate branching systems otherwise similar to the sterile examples.
The entire plant up to the second or third divisions of the ultimate branching systems is covered with fine spines.
Above & Below: Anapaulia moodyi reconstruction
Arachnoxylon †
Arachnoxylon †
Read, 1938
Middle Devonian of New York
Anatomically preserved stem fragments with a ribbed protostele of only primary tissues.
A strand of protoxylem or a cavity that resembles a peripheral loop at the end of each xylem arm
Laterals were produced in whorls
Primary xylem was mesarch, with secondary wall thickenings that were scalariform to circular, elliptical bordered pits
A. kopfii †
Arnold, 1935
Givetian of New York
6-7 xylem strands in cross-section
A. minor †
Stein et al., 1983
Xylem strand is X- or H-shaped in transverse section
Asteropteris noveboracensis †
Asteropteris noveboracensis †
Dawson, 1881; Bertrand, 1913; Sebby, 1972
A stellate protostele with conspicuous permanent protoxylem strands (Bertrand, 1913)
Traces are tetrapolar and arranged in a very shallow helix.
Compsocradus †
Compsocradus †
Devonian of Venezuela (probably Givetian or possibly late Eifelian/ early Frasnian)
Morphology
Plants pseudomonopodial, with at least three orders of axes known. Lower orders of axes bear both higher-order axes and dichotomous appendages. Ultimate appendages consisting of narrow axes branched predominantly isotomously, successive dichotomies being approximately perpendicular
External surfaces lacking emergences
Fertile appendages terminate in erect or recurved paired sporangia. Sterile ultimate appendages terminate with oppositely recurved tips.
Both ultimate appendages and second-order axes are arranged in loose whorls on first-order axes, with attachments alternating in successive whorls; insertion patterns become less clear in higher-order axes.
Anatomy
Protostele ribbed, mesarch, with six primary xylem ribs; traces arising from every other rib at each whorl, successive whorls alternating; a similar pattern inferred from compression material, some branches and appendages in whorls may occur in neighboring ranks, up to 10 ranks on the largest axes.
Protoxylem strands located permanently peripherally, one in each primary xylem rib; tracheids with uniseriate circular to oval bordered pits.
C. laevigatus †
Venezuela
C. givetianus †
Xinjiang, China
Previously named Rhamophyton givetianum (Wang, 2008)
Above, left (a): Compsocradus laevigatus † (Berry & Stein 2000); Above, Center (c) & Right (d): Compsocradus givetianus † (Fu et al 2011)
Ibyka †
Ibyka †
Middle - Late Devonian of New York
Known from anatomy and morphology
At least three orders of branching are known
Insertions of laterals are dominantly whorled, sometimes imperfectly, with distinct internodes
Within a whorl, branches may substitute for dichotomous appendages, with the latter more numerous
I. amphikoma †
Skog & Banks, 1973; Berry et al., 2022
I. vogtii †
Hoeg, 1942; Berry, 2005
Above: Reconstruction of Ibyka amphikoma (Berry et al. 2022)
Iridopteris eriensis †
Iridopteris eriensis †
Middle Devonian of North America (New York)
Arnold, 1940
Permineralized stems possess a five-ribbed protostele with mesarch xylem
The axes are 5.5 cm in diameter and characterized by two types of traces (Stein, 1982)
Minor traces are circular in transverse section and produced by radial divisions at the periphery of the primary ribs in a regular, alternate pattern.
Larger (major) traces are elliptical in cross-section with a protoxylem strand at each end
Although Iridopteris and Arachnoxylon are similar, the bilateral symmetry and smaller size of Iridopteris are the main features that distinguish these two taxa
Keraphyton mawsoniae †
Keraphyton mawsoniae †
Stem up to 20 mm in diameter, with primary tissues only.
Vascular system actinostelic, consisting of four fundamental ribs united to a central segment.
Fundamental ribs branching unequally, one branch dividing into two equal ultimate ribs, the other dividing in more ultimate ribs of distally decreasing dimensions.
Protoxylem strands exarch to mesarch, at tip of ultimate ribs. Metaxylem tracheids from 20 to 140 mm in diameter, the smallest ones arranged in 1-2 layers along the lateral edges of the ribs.
Tracheid walls showing scalariform to multiseriate bordered pit pairs with elliptical apertures.
Endodermis-like cells consisting of rectangular cells up to 200 mm high and 120 mm periclinally.
Inner cortical cells up to 160 mm in diameter, thin-walled, polygonal to circular in transverse section, with transverse to oblique endwalls in longitudinal section.
Outer cortex homogeneous, with cells becoming thicker-walled and narrower towards periphery.
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